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Concept
Ramanujan's congruences
Summary
In mathematics, Ramanujan's congruences are some remarkable congruences for the partition function p(n). The mathematician Srinivasa Ramanujan discovered the congruences
This means that:
If a number is 4 more than a multiple of 5, i.e. it is in the sequence
4, 9, 14, 19, 24, 29, . . .
then the number of its partitions is a multiple of 5.
If a number is 5 more than a multiple of 7, i.e. it is in the sequence
5, 12, 19, 26, 33, 40, . . .
then the number of its partitions is a multiple of 7.
If a number is 6 more than a multiple of 11, i.e. it is in the sequence
6, 17, 28, 39, 50, 61, . . .
then the number of its partitions is a multiple of 11.
In his 1919 paper, he proved the first two congruences using the following identities (using q-Pochhammer symbol notation):
He then stated that "It appears there are no equally simple properties for any moduli involving primes other than these".
After Ramanujan died in 1920, G. H. Hardy extracted proofs of all three congruences from an unpublished manuscript of Ramanujan on p(n) (Ramanujan, 1921). The proof in this manuscript employs the Eisenstein series.
In 1944, Freeman Dyson defined the rank function and conjectured the existence of a crank function for partitions that would provide a combinatorial proof of Ramanujan's congruences modulo 11. Forty years later, George Andrews and Frank Garvan found such a function, and proved the celebrated result that the crank simultaneously "explains" the three Ramanujan congruences modulo 5, 7 and 11.
In the 1960s, A. O. L. Atkin of the University of Illinois at Chicago discovered additional congruences for small prime moduli. For example:
Extending the results of A. Atkin, Ken Ono in 2000 proved that there are such Ramanujan congruences modulo every integer coprime to 6. For example, his results give
Later Ken Ono conjectured that the elusive crank also satisfies exactly the same types of general congruences. This was proved by his Ph.D. student Karl Mahlburg in his 2005 paper Partition Congruences and the Andrews–Garvan–Dyson Crank, linked below.
Official source
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