21656051 has 4 divisors (see below), whose sum is σ = 21858552. Its totient is φ = 21453552.

The previous prime is 21656039. The next prime is 21656057. The reversal of 21656051 is 15065612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21656051 - 2⁶ = 21655987 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21656051.

It is not an unprimeable number, because it can be changed into a prime (21656057) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 101090 + ... + 101303.

It is an arithmetic number, because the mean of its divisors is an integer number (5464638).

Almost surely, 2^21656051 is an apocalyptic number.

21656051 is a deficient number, since it is larger than the sum of its proper divisors (202501).

21656051 is a wasteful number, since it uses less digits than its factorization.

21656051 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 202500.

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 21656051 is about 4653.6062360281. The cubic root of 21656051 is about 278.7360161096.

The spelling of 21656051 in words is "twenty-one million, six hundred fifty-six thousand, fifty-one".