21991624 has 8 divisors (see below), whose sum is σ = 41234310. Its totient is φ = 10995808.

The previous prime is 21991589. The next prime is 21991631. The reversal of 21991624 is 42619912.

It can be written as a sum of positive squares in only one way, i.e., 19980900 + 2010724 = 4470^2 + 1418^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is a super-3 number, since 3×21991624³ (a number of 23 digits) contains 333 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21991624.

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 as a sum of consecutive naturals, namely, 1374469 + ... + 1374484.

Almost surely, 2^21991624 is an apocalyptic number.

It is an amenable number.

21991624 is a deficient number, since it is larger than the sum of its proper divisors (19242686).

21991624 is a wasteful number, since it uses less digits than its factorization.

21991624 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2748959 (or 2748955 counting only the distinct ones).

The product of its digits is 7776, while the sum is 34.

The square root of 21991624 is about 4689.5227902208. The cubic root of 21991624 is about 280.1683681252.

The spelling of 21991624 in words is "twenty-one million, nine hundred ninety-one thousand, six hundred twenty-four".