21251656 has 8 divisors (see below), whose sum is σ = 39846870. Its totient is φ = 10625824.

The previous prime is 21251617. The next prime is 21251669. The reversal of 21251656 is 65615212.

It can be written as a sum of positive squares in only one way, i.e., 15729156 + 5522500 = 3966^2 + 2350^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1328221 + ... + 1328236.

Almost surely, 2^21251656 is an apocalyptic number.

It is an amenable number.

21251656 is a deficient number, since it is larger than the sum of its proper divisors (18595214).

21251656 is a wasteful number, since it uses less digits than its factorization.

21251656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2656463 (or 2656459 counting only the distinct ones).

The product of its digits is 3600, while the sum is 28.

The square root of 21251656 is about 4609.9518435663. The cubic root of 21251656 is about 276.9901076893.

Adding to 21251656 its reverse (65615212), we get a palindrome (86866868).

The spelling of 21251656 in words is "twenty-one million, two hundred fifty-one thousand, six hundred fifty-six".