21387951 has 12 divisors (see below), whose sum is σ = 33270328. Its totient is φ = 13161744.

The previous prime is 21387931. The next prime is 21387959. The reversal of 21387951 is 15978312.

It is not a de Polignac number, because 21387951 - 2⁷ = 21387823 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21387959) 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, 91285 + ... + 91518.

Almost surely, 2^21387951 is an apocalyptic number.

21387951 is a deficient number, since it is larger than the sum of its proper divisors (11882377).

21387951 is a wasteful number, since it uses less digits than its factorization.

21387951 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 182822 (or 182819 counting only the distinct ones).

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

The square root of 21387951 is about 4624.7109098840. The cubic root of 21387951 is about 277.5809941324.

The spelling of 21387951 in words is "twenty-one million, three hundred eighty-seven thousand, nine hundred fifty-one".