21987666 has 16 divisors (see below), whose sum is σ = 48861600. Its totient is φ = 7329204.

The previous prime is 21987631. The next prime is 21987671. The reversal of 21987666 is 66678912.

It is a super-2 number, since 2×21987666² = 966914912255112, which contains 22 as substring.

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, 203536 + ... + 203643.

It is an arithmetic number, because the mean of its divisors is an integer number (3053850).

Almost surely, 2^21987666 is an apocalyptic number.

21987666 is an abundant number, since it is smaller than the sum of its proper divisors (26873934).

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

21987666 is a wasteful number, since it uses less digits than its factorization.

21987666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 407190 (or 407184 counting only the distinct ones).

The product of its digits is 217728, while the sum is 45.

The square root of 21987666 is about 4689.1007666716. The cubic root of 21987666 is about 280.1515591054.

The spelling of 21987666 in words is "twenty-one million, nine hundred eighty-seven thousand, six hundred sixty-six".