21156681 has 24 divisors (see below), whose sum is σ = 35341824. Its totient is φ = 11158560.

The previous prime is 21156661. The next prime is 21156701. The reversal of 21156681 is 18665112.

It is an interprime number because it is at equal distance from previous prime (21156661) and next prime (21156701).

It is a de Polignac number, because none of the positive numbers 2^k-21156681 is a prime.

It is a super-2 number, since 2×21156681² = 895210301871522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21156661) by changing a digit.

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 23 ways as a sum of consecutive naturals, for example, 3625 + ... + 7446.

It is an arithmetic number, because the mean of its divisors is an integer number (1472576).

Almost surely, 2^21156681 is an apocalyptic number.

21156681 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21156681 is a deficient number, since it is larger than the sum of its proper divisors (14185143).

21156681 is a wasteful number, since it uses less digits than its factorization.

21156681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11101 (or 11094 counting only the distinct ones).

The product of its digits is 2880, while the sum is 30.

The square root of 21156681 is about 4599.6392249828. The cubic root of 21156681 is about 276.5768626778.

The spelling of 21156681 in words is "twenty-one million, one hundred fifty-six thousand, six hundred eighty-one".