21513978 has 16 divisors (see below), whose sum is σ = 47808960. Its totient is φ = 7171308.

The previous prime is 21513967. The next prime is 21513979. The reversal of 21513978 is 87931512.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21513979) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 199150 + ... + 199257.

It is an arithmetic number, because the mean of its divisors is an integer number (2988060).

Almost surely, 2^21513978 is an apocalyptic number.

21513978 is an abundant number, since it is smaller than the sum of its proper divisors (26294982).

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

21513978 is a wasteful number, since it uses less digits than its factorization.

21513978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 398418 (or 398412 counting only the distinct ones).

The product of its digits is 15120, while the sum is 36.

The square root of 21513978 is about 4638.3162893447. The cubic root of 21513978 is about 278.1251355973.

The spelling of 21513978 in words is "twenty-one million, five hundred thirteen thousand, nine hundred seventy-eight".