21656551 has 8 divisors (see below), whose sum is σ = 24794624. Its totient is φ = 18529560.

The previous prime is 21656543. The next prime is 21656597. The reversal of 21656551 is 15565612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21656551 - 2³ = 21656543 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21656251) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1966 + ... + 6868.

It is an arithmetic number, because the mean of its divisors is an integer number (3099328).

Almost surely, 2^21656551 is an apocalyptic number.

21656551 is a deficient number, since it is larger than the sum of its proper divisors (3138073).

21656551 is an equidigital number, since it uses as much as digits as its factorization.

21656551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5541.

The product of its digits is 9000, while the sum is 31.

The square root of 21656551 is about 4653.6599574958. The cubic root of 21656551 is about 278.7381612673.

The spelling of 21656551 in words is "twenty-one million, six hundred fifty-six thousand, five hundred fifty-one".