21156551 has 8 divisors (see below), whose sum is σ = 24124464. Its totient is φ = 18380160.

The previous prime is 21156529. The next prime is 21156589. The reversal of 21156551 is 15565112.

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

It is a cyclic number.

It is not a de Polignac number, because 21156551 - 2¹⁴ = 21140167 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21156551.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21156511) 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, 47645 + ... + 48086.

It is an arithmetic number, because the mean of its divisors is an integer number (3015558).

Almost surely, 2^21156551 is an apocalyptic number.

21156551 is a deficient number, since it is larger than the sum of its proper divisors (2967913).

21156551 is a wasteful number, since it uses less digits than its factorization.

21156551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 95761.

The product of its digits is 1500, while the sum is 26.

The square root of 21156551 is about 4599.6250934179. The cubic root of 21156551 is about 276.5762961890.

The spelling of 21156551 in words is "twenty-one million, one hundred fifty-six thousand, five hundred fifty-one".