21624981 has 16 divisors (see below), whose sum is σ = 34089600. Its totient is φ = 11930688.

The previous prime is 21624973. The next prime is 21625027. The reversal of 21624981 is 18942612.

It is not a de Polignac number, because 21624981 - 2³ = 21624973 is a prime.

It is a super-2 number, since 2×21624981² = 935279606500722, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21624971) 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, 17146 + ... + 18363.

It is an arithmetic number, because the mean of its divisors is an integer number (2130600).

Almost surely, 2^21624981 is an apocalyptic number.

21624981 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21624981 is a deficient number, since it is larger than the sum of its proper divisors (12464619).

21624981 is a wasteful number, since it uses less digits than its factorization.

21624981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35548.

The product of its digits is 6912, while the sum is 33.

The square root of 21624981 is about 4650.2667665415. The cubic root of 21624981 is about 278.6026511825.

The spelling of 21624981 in words is "twenty-one million, six hundred twenty-four thousand, nine hundred eighty-one".