20656640 has 40 divisors (see below), whose sum is σ = 49533660. Its totient is φ = 8261632.

The previous prime is 20656639. The next prime is 20656679. The reversal of 20656640 is 4665602.

It can be written as a sum of positive squares in 2 ways, for example, as 16908544 + 3748096 = 4112^2 + 1936^2 .

It is a tau number, because it is divible by the number of its divisors (40).

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1475 + ... + 6594.

Almost surely, 2^20656640 is an apocalyptic number.

20656640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20656640 is an abundant number, since it is smaller than the sum of its proper divisors (28877020).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20656640 is an frugal number, since it uses more digits than its factorization.

20656640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8092 (or 8076 counting only the distinct ones).

The product of its (nonzero) digits is 8640, while the sum is 29.

The square root of 20656640 is about 4544.9576455672. The cubic root of 20656640 is about 274.3804897347.

The spelling of 20656640 in words is "twenty million, six hundred fifty-six thousand, six hundred forty".