21515564257 has 16 divisors (see below), whose sum is σ = 23868043200. Its totient is φ = 19231632640.

The previous prime is 21515564233. The next prime is 21515564281. The reversal of 21515564257 is 75246551512.

It is an interprime number because it is at equal distance from previous prime (21515564233) and next prime (21515564281).

It is not a de Polignac number, because 21515564257 - 2¹⁵ = 21515531489 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21515564297) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 113853 + ... + 236629.

It is an arithmetic number, because the mean of its divisors is an integer number (1491752700).

Almost surely, 2^21515564257 is an apocalyptic number.

It is an amenable number.

21515564257 is a deficient number, since it is larger than the sum of its proper divisors (2352478943).

21515564257 is a wasteful number, since it uses less digits than its factorization.

21515564257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 123056.

The product of its digits is 420000, while the sum is 43.

The spelling of 21515564257 in words is "twenty-one billion, five hundred fifteen million, five hundred sixty-four thousand, two hundred fifty-seven".