21566451 has 16 divisors (see below), whose sum is σ = 29611008. Its totient is φ = 13953600.

The previous prime is 21566437. The next prime is 21566453. The reversal of 21566451 is 15466512.

It is not a de Polignac number, because 21566451 - 2⁷ = 21566323 is a prime.

It is a super-2 number, since 2×21566451² = 930223617470802, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21566453) 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 15 ways as a sum of consecutive naturals, for example, 33010 + ... + 33656.

It is an arithmetic number, because the mean of its divisors is an integer number (1850688).

Almost surely, 2^21566451 is an apocalyptic number.

21566451 is a deficient number, since it is larger than the sum of its proper divisors (8044557).

21566451 is a wasteful number, since it uses less digits than its factorization.

21566451 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 962.

The product of its digits is 7200, while the sum is 30.

The square root of 21566451 is about 4643.9693151441. The cubic root of 21566451 is about 278.3510695030.

It can be divided in two parts, 215 and 66451, that added together give a palindrome (66666).

The spelling of 21566451 in words is "twenty-one million, five hundred sixty-six thousand, four hundred fifty-one".