21138957 has 12 divisors (see below), whose sum is σ = 34896160. Its totient is φ = 12079368.

The previous prime is 21138937. The next prime is 21138959. The reversal of 21138957 is 75983112.

It is not a de Polignac number, because 21138957 - 2¹⁹ = 20614669 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21138959) 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, 167707 + ... + 167832.

Almost surely, 2^21138957 is an apocalyptic number.

It is an amenable number.

21138957 is a deficient number, since it is larger than the sum of its proper divisors (13757203).

21138957 is a wasteful number, since it uses less digits than its factorization.

21138957 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 335552 (or 335549 counting only the distinct ones).

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

The square root of 21138957 is about 4597.7121484495. The cubic root of 21138957 is about 276.4996070526.

The spelling of 21138957 in words is "twenty-one million, one hundred thirty-eight thousand, nine hundred fifty-seven".