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An Introduction to Number Theory

By Prof. Somnath Jha   |   IIT Kanpur
Learners enrolled: 781   |  Exam registration: 61
ABOUT THE COURSE:

This course aims to introduce some basic topics in number theory. We will study quadratic number fields focusing on the structure of prime ideals and units in the ring of integers of the field. We will use binary quadratic forms to measure the failure of unique factorisation in the ring of integers of imaginary quadratic fields. Further, we will study classical Diophantine problems related to congruent numbers and rational cube sums and their relation with elliptic curves. Along the way, we will recall some basic concepts from abstract algebra which are required in this course.

INTENDED AUDIENCE: BS/BSc/BMATH/MSc/MMATH

PREREQUISITES: Familiarity with basic linear algebra will be useful.

INDUSTRY SUPPORT: The topics in this course are relevant to Cryptography and Cybersecurity.
Summary
Course Status : Ongoing
Course Type : Elective
Language for course content : English
Duration : 12 weeks
Category :
  • Mathematics
Credit Points : 3
Level : Undergraduate
Start Date : 19 Jan 2026
End Date : 10 Apr 2026
Enrollment Ends : 02 Feb 2026
Exam Registration Ends : 20 Feb 2026
Exam Date : 26 Apr 2026 IST
NCrF Level   : 4.5 — 8.0

Note: This exam date is subject to change based on seat availability. You can check final exam date on your hall ticket.


Page Visits



Course layout

Week 1: Abelian groups, subgroups and quotient groups, finite abelian groups and finitely generated abelian groups

Week 2: Commutative Rings, ideals, fields, Polynomial rings, zero sets of ideals in polynomial rings.

Week 3: The groups Z/nZ and (Z/nZ)*, Euler’s theorem and Wilson Theorem. Chinese Remainder Theorem,

Week 4: Classification of finite fields, the multiplicative subgroup of a finite field,

Week 5: Law of quadratic reciprocity, Quadratic fields, Containment of quadratic fields inside cyclotomic fields

Week 6: UFD and PID, Ring of integers of quadratic fields, Various examples.

Week 7: 
Binary quadratic forms

Week 8: 
Ideal class groups of imaginary quadratic fields

Week 9: 
Units in the ring of integers of quadratic fields, Diophantine problem: Bramhagupta-Pell’s equation

Week 10: Infinite descent, n=4 case of the Fermat’s Last Theorem, Diophantine problem of congruent numbers, relation with elliptic curves

Week 11: 
Diophantine problem on rational cube sums, relation with elliptic curves

Week 12: 
Group law of elliptic curves, statements of Nagell-Lutz Theorem and Mordell-Weil Theorem

Books and references

  1. A Friendly Introduction to Number Theory, J. H. Silverman, Pearson Prentice Hall, 2006.
  2. A Classical Introduction to Modern Number Theory, K. Ireland, M. Rosen, Springer GTM.
  3. An introduction to the Theory of Numbers,I. Niven, H. S. Zuckerman, H. L. Montgomery, Wiley.
  4. An Introduction to the Theory of Numbers. G. H. Hardy, E. M. Wright, Oxford.
  5. Abstract Algebra, D. S. Dummit, R. M. Foote, Wiley.
  6. Rational points on elliptic curves, J. H. Silverman and J. Tate, Springer UTM.
  7. Introduction to elliptic curves and modular forms, N. Koblitz, Springer-Verlag GTM.
  8. A course in arithmetic, J. P. Serre, Springer-Verlag GTM.

Instructor bio

Prof. Somnath Jha

IIT Kanpur
Prof. Somnath Jha obtained his PhD from Tata Institute of Fundamental Research, Mumbai in 2012. He has worked as a MATCH postdoctoral researcher at University of Heidelberg, Germany and as a JSPS postdoctoral fellow at Osaka University, Japan. At present, he is an associate professor at the Department of Mathematics and Statistics at IIT Kanpur. The broad areas of his research are number theory and arithmetic geometry. He is interested in problems related to Iwasawa theory of elliptic curves and modular forms and Diophantine problems related to congruent numbers and rational cube sums.

Course certificate

The course is free to enroll and learn from. But if you want a certificate, you have to register and write the proctored exam conducted by us in person at any of the designated exam centres.
The exam is optional for a fee of Rs 1000/- (Rupees one thousand only).
Date and Time of Exams: April 26, 2026 Morning session 9am to 12 noon; Afternoon Session 2pm to 5pm.
Registration url: Announcements will be made when the registration form is open for registrations.
The online registration form has to be filled and the certification exam fee needs to be paid. More details will be made available when the exam registration form is published. If there are any changes, it will be mentioned then.
Please check the form for more details on the cities where the exams will be held, the conditions you agree to when you fill the form etc.

CRITERIA TO GET A CERTIFICATE

Average assignment score = 25% of average of best 8 assignments out of the total 12 assignments given in the course.
Exam score = 75% of the proctored certification exam score out of 100

Final score = Average assignment score + Exam score

Please note that assignments encompass all types (including quizzes, programming tasks, and essay submissions) available in the specific week.

YOU WILL BE ELIGIBLE FOR A CERTIFICATE ONLY IF AVERAGE ASSIGNMENT SCORE >=10/25 AND EXAM SCORE >= 30/75. If one of the 2 criteria is not met, you will not get the certificate even if the Final score >= 40/100.

Certificate will have your name, photograph and the score in the final exam with the breakup.It will have the logos of NPTEL and IIT Kanpur .It will be e-verifiable at nptel.ac.in/noc.

Only the e-certificate will be made available. Hard copies will not be dispatched.

Once again, thanks for your interest in our online courses and certification. Happy learning.

- NPTEL team
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