21015505251 has 48 divisors (see below), whose sum is σ = 33345932256. Its totient is φ = 12674009088.

The previous prime is 21015505249. The next prime is 21015505253. The reversal of 21015505251 is 15250551012.

21015505251 is a `hidden beast` number, since 2 + 10 + 1 + 550 + 52 + 51 = 666.

It is an interprime number because it is at equal distance from previous prime (21015505249) and next prime (21015505253).

It is not a de Polignac number, because 21015505251 - 2¹ = 21015505249 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21015505253) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 8103411 + ... + 8106003.

It is an arithmetic number, because the mean of its divisors is an integer number (694706922).

Almost surely, 2^21015505251 is an apocalyptic number.

21015505251 is a deficient number, since it is larger than the sum of its proper divisors (12330427005).

21015505251 is a wasteful number, since it uses less digits than its factorization.

21015505251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3972 (or 3969 counting only the distinct ones).

The product of its (nonzero) digits is 2500, while the sum is 27.

The spelling of 21015505251 in words is "twenty-one billion, fifteen million, five hundred five thousand, two hundred fifty-one".