21543651 has 12 divisors (see below), whose sum is σ = 32271512. Its totient is φ = 14362272.

The previous prime is 21543619. The next prime is 21543653. The reversal of 21543651 is 15634512.

21543651 is a `hidden beast` number, since 2 + 1 + 5 + 4 + 3 + 651 = 666.

It is not a de Polignac number, because 21543651 - 2⁵ = 21543619 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21543653) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 44086 + ... + 44571.

Almost surely, 2^21543651 is an apocalyptic number.

21543651 is a deficient number, since it is larger than the sum of its proper divisors (10727861).

21543651 is an frugal number, since it uses more digits than its factorization.

21543651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 88672 (or 88660 counting only the distinct ones).

The product of its digits is 3600, while the sum is 27.

The square root of 21543651 is about 4641.5138694180. The cubic root of 21543651 is about 278.2529442224.

The spelling of 21543651 in words is "twenty-one million, five hundred forty-three thousand, six hundred fifty-one".