21631645 has 16 divisors (see below), whose sum is σ = 30624768. Its totient is φ = 14353920.

The previous prime is 21631639. The next prime is 21631663. The reversal of 21631645 is 54613612.

It is not a de Polignac number, because 21631645 - 2⁷ = 21631517 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8884 + ... + 11053.

It is an arithmetic number, because the mean of its divisors is an integer number (1914048).

Almost surely, 2^21631645 is an apocalyptic number.

It is an amenable number.

21631645 is a deficient number, since it is larger than the sum of its proper divisors (8993123).

21631645 is a wasteful number, since it uses less digits than its factorization.

21631645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19980.

The product of its digits is 4320, while the sum is 28.

The square root of 21631645 is about 4650.9832293828. The cubic root of 21631645 is about 278.6312665045.

The spelling of 21631645 in words is "twenty-one million, six hundred thirty-one thousand, six hundred forty-five".