20978664 has 48 divisors (see below), whose sum is σ = 61012800. Its totient is φ = 5993568.

The previous prime is 20978623. The next prime is 20978669. The reversal of 20978664 is 46687902.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is not an unprimeable number, because it can be changed into a prime (20978669) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 7744 + ... + 10095.

It is an arithmetic number, because the mean of its divisors is an integer number (1271100).

Almost surely, 2^20978664 is an apocalyptic number.

20978664 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

20978664 is an abundant number, since it is smaller than the sum of its proper divisors (40034136).

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

20978664 is a wasteful number, since it uses less digits than its factorization.

20978664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17862 (or 17851 counting only the distinct ones).

The product of its (nonzero) digits is 145152, while the sum is 42.

The square root of 20978664 is about 4580.2471549033. The cubic root of 20978664 is about 275.7989504113.

The spelling of 20978664 in words is "twenty million, nine hundred seventy-eight thousand, six hundred sixty-four".