21551660 has 24 divisors (see below), whose sum is σ = 48740496. Its totient is φ = 7957440.

The previous prime is 21551657. The next prime is 21551671. The reversal of 21551660 is 6615512.

It is a Harshad number since it is a multiple of its sum of digits (26).

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 7 ways as a sum of consecutive naturals, for example, 41186 + ... + 41705.

It is an arithmetic number, because the mean of its divisors is an integer number (2030854).

Almost surely, 2^21551660 is an apocalyptic number.

21551660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21551660 is an abundant number, since it is smaller than the sum of its proper divisors (27188836).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21551660 is a wasteful number, since it uses less digits than its factorization.

21551660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 82913 (or 82911 counting only the distinct ones).

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 21551660 is about 4642.3765465546. The cubic root of 21551660 is about 278.2874207638.

The spelling of 21551660 in words is "twenty-one million, five hundred fifty-one thousand, six hundred sixty".