21621986 has 24 divisors (see below), whose sum is σ = 34190100. Its totient is φ = 10251072.

The previous prime is 21621967. The next prime is 21621997. The reversal of 21621986 is 68912612.

It can be written as a sum of positive squares in 6 ways, for example, as 17799961 + 3822025 = 4219^2 + 1955^2 .

It is a Curzon 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 in 11 ways as a sum of consecutive naturals, for example, 145040 + ... + 145188.

Almost surely, 2^21621986 is an apocalyptic number.

21621986 is the 2486-th centered heptagonal number.

21621986 is a deficient number, since it is larger than the sum of its proper divisors (12568114).

21621986 is a wasteful number, since it uses less digits than its factorization.

21621986 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 278 (or 241 counting only the distinct ones).

The product of its digits is 10368, while the sum is 35.

The square root of 21621986 is about 4649.9447308543. The cubic root of 21621986 is about 278.5897886900.

The spelling of 21621986 in words is "twenty-one million, six hundred twenty-one thousand, nine hundred eighty-six".