21089864 has 8 divisors (see below), whose sum is σ = 39543510. Its totient is φ = 10544928.

The previous prime is 21089863. The next prime is 21089879. The reversal of 21089864 is 46898012.

It can be written as a sum of positive squares in only one way, i.e., 16467364 + 4622500 = 4058^2 + 2150^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is not an unprimeable number, because it can be changed into a prime (21089863) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1318109 + ... + 1318124.

Almost surely, 2^21089864 is an apocalyptic number.

It is an amenable number.

21089864 is a deficient number, since it is larger than the sum of its proper divisors (18453646).

21089864 is a wasteful number, since it uses less digits than its factorization.

21089864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2636239 (or 2636235 counting only the distinct ones).

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

The square root of 21089864 is about 4592.3701941372. The cubic root of 21089864 is about 276.2853940714.

The spelling of 21089864 in words is "twenty-one million, eighty-nine thousand, eight hundred sixty-four".