20656639 has 2 divisors, whose sum is σ = 20656640. Its totient is φ = 20656638.

The previous prime is 20656631. The next prime is 20656679. The reversal of 20656639 is 93665602.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20656639 - 2³ = 20656631 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 20656598 and 20656607.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20656631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10328319 + 10328320.

It is an arithmetic number, because the mean of its divisors is an integer number (10328320).

Almost surely, 2^20656639 is an apocalyptic number.

20656639 is a deficient number, since it is larger than the sum of its proper divisors (1).

20656639 is an equidigital number, since it uses as much as digits as its factorization.

20656639 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 58320, while the sum is 37.

The square root of 20656639 is about 4544.9575355552. The cubic root of 20656639 is about 274.3804853071.

The spelling of 20656639 in words is "twenty million, six hundred fifty-six thousand, six hundred thirty-nine".