21640988 has 12 divisors (see below), whose sum is σ = 37932720. Its totient is φ = 10803072.

The previous prime is 21640987. The next prime is 21641003. The reversal of 21640988 is 88904612.

It is a super-2 number, since 2×21640988² = 936664723232288, which contains 22 as substring.

It is a hoax number, since the sum of its digits (38) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21640987) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1328 + ... + 6711.

It is an arithmetic number, because the mean of its divisors is an integer number (3161060).

Almost surely, 2^21640988 is an apocalyptic number.

It is an amenable number.

21640988 is a deficient number, since it is larger than the sum of its proper divisors (16291732).

21640988 is a wasteful number, since it uses less digits than its factorization.

21640988 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8716 (or 8714 counting only the distinct ones).

The product of its (nonzero) digits is 27648, while the sum is 38.

The square root of 21640988 is about 4651.9875322275. The cubic root of 21640988 is about 278.6713756012.

The spelling of 21640988 in words is "twenty-one million, six hundred forty thousand, nine hundred eighty-eight".