21157656 has 64 divisors (see below), whose sum is σ = 60328800. Its totient is φ = 6125568.

The previous prime is 21157649. The next prime is 21157693. The reversal of 21157656 is 65675112.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3310 + ... + 7298.

Almost surely, 2^21157656 is an apocalyptic number.

21157656 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21157656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30164400).

21157656 is an abundant number, since it is smaller than the sum of its proper divisors (39171144).

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

21157656 is a wasteful number, since it uses less digits than its factorization.

21157656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4028 (or 4024 counting only the distinct ones).

The product of its digits is 12600, while the sum is 33.

The square root of 21157656 is about 4599.7452103350. The cubic root of 21157656 is about 276.5811112695.

The spelling of 21157656 in words is "twenty-one million, one hundred fifty-seven thousand, six hundred fifty-six".