21621556 has 24 divisors (see below), whose sum is σ = 41469120. Its totient is φ = 9782400.

The previous prime is 21621547. The next prime is 21621557. The reversal of 21621556 is 65512612.

It is a super-2 number, since 2×21621556² = 934983367722272, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21621557) 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 7 ways as a sum of consecutive naturals, for example, 9585 + ... + 11623.

It is an arithmetic number, because the mean of its divisors is an integer number (1727880).

Almost surely, 2^21621556 is an apocalyptic number.

It is an amenable number.

21621556 is a deficient number, since it is larger than the sum of its proper divisors (19847564).

21621556 is a wasteful number, since it uses less digits than its factorization.

21621556 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2295 (or 2293 counting only the distinct ones).

The product of its digits is 3600, while the sum is 28.

The square root of 21621556 is about 4649.8984935157. The cubic root of 21621556 is about 278.5879418908.

The spelling of 21621556 in words is "twenty-one million, six hundred twenty-one thousand, five hundred fifty-six".