21805972 has 6 divisors (see below), whose sum is σ = 38160458. Its totient is φ = 10902984.

The previous prime is 21805967. The next prime is 21805981. The reversal of 21805972 is 27950812.

It can be written as a sum of positive squares in only one way, i.e., 19483396 + 2322576 = 4414^2 + 1524^2 .

It is a congruent number.

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 2725743 + ... + 2725750.

Almost surely, 2^21805972 is an apocalyptic number.

It is an amenable number.

21805972 is a deficient number, since it is larger than the sum of its proper divisors (16354486).

21805972 is a wasteful number, since it uses less digits than its factorization.

21805972 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5451497 (or 5451495 counting only the distinct ones).

The product of its (nonzero) digits is 10080, while the sum is 34.

The square root of 21805972 is about 4669.6864991132. The cubic root of 21805972 is about 279.3777508417.

The spelling of 21805972 in words is "twenty-one million, eight hundred five thousand, nine hundred seventy-two".