21315987 has 32 divisors (see below), whose sum is σ = 39375360. Its totient is φ = 11072160.

The previous prime is 21315961. The next prime is 21315989. The reversal of 21315987 is 78951312.

It is not a de Polignac number, because 21315987 - 2⁶ = 21315923 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21315989) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 3048 + ... + 7205.

It is an arithmetic number, because the mean of its divisors is an integer number (1230480).

Almost surely, 2^21315987 is an apocalyptic number.

21315987 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

21315987 is a deficient number, since it is larger than the sum of its proper divisors (18059373).

21315987 is a wasteful number, since it uses less digits than its factorization.

21315987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10280 (or 10274 counting only the distinct ones).

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

The square root of 21315987 is about 4616.9239759823. The cubic root of 21315987 is about 277.2693188834.

It can be divided in two parts, 2131 and 5987, that added together give a palindrome (8118).

The spelling of 21315987 in words is "twenty-one million, three hundred fifteen thousand, nine hundred eighty-seven".