21513987 has 12 divisors (see below), whose sum is σ = 33900984. Its totient is φ = 13038720.

The previous prime is 21513979. The next prime is 21514013. The reversal of 21513987 is 78931512.

It is not a de Polignac number, because 21513987 - 2³ = 21513979 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21513967) 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, 108558 + ... + 108755.

It is an arithmetic number, because the mean of its divisors is an integer number (2825082).

Almost surely, 2^21513987 is an apocalyptic number.

21513987 is a deficient number, since it is larger than the sum of its proper divisors (12386997).

21513987 is a wasteful number, since it uses less digits than its factorization.

21513987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 217330 (or 217327 counting only the distinct ones).

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

The square root of 21513987 is about 4638.3172595242. The cubic root of 21513987 is about 278.1251743802.

It can be divided in two parts, 21513 and 987, that added together give a square (22500 = 150²).

The spelling of 21513987 in words is "twenty-one million, five hundred thirteen thousand, nine hundred eighty-seven".