21876561 has 32 divisors (see below), whose sum is σ = 37523200. Its totient is φ = 12492144.

The previous prime is 21876553. The next prime is 21876587. The reversal of 21876561 is 16567812.

21876561 is a `hidden beast` number, since 21 + 8 + 76 + 561 = 666.

It is not a de Polignac number, because 21876561 - 2³ = 21876553 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

21876561 is a modest number, since divided by 6561 gives 2187 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21876511) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 14595 + ... + 16023.

It is an arithmetic number, because the mean of its divisors is an integer number (1172600).

Almost surely, 2^21876561 is an apocalyptic number.

21876561 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21876561 is a deficient number, since it is larger than the sum of its proper divisors (15646639).

21876561 is an frugal number, since it uses more digits than its factorization.

21876561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1457 (or 1439 counting only the distinct ones).

The product of its digits is 20160, while the sum is 36.

The square root of 21876561 is about 4677.2386084099. The cubic root of 21876561 is about 279.6788878324.

It can be divided in two parts, 2187 and 6561, that multiplied together give a 15-th power (14348907 = 3¹⁵).

The spelling of 21876561 in words is "twenty-one million, eight hundred seventy-six thousand, five hundred sixty-one".