521618391 has 12 divisors (see below), whose sum is σ = 861084432. Its totient is φ = 298067616.

The previous prime is 521618371. The next prime is 521618393. The reversal of 521618391 is 193816125.

521618391 is a `hidden beast` number, since 5 + 2 + 1 + 618 + 39 + 1 = 666.

It is not a de Polignac number, because 521618391 - 2¹⁰ = 521617367 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (521618393) 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, 4139766 + ... + 4139891.

It is an arithmetic number, because the mean of its divisors is an integer number (71757036).

Almost surely, 2^521618391 is an apocalyptic number.

521618391 is a deficient number, since it is larger than the sum of its proper divisors (339466041).

521618391 is a wasteful number, since it uses less digits than its factorization.

521618391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8279670 (or 8279667 counting only the distinct ones).

The product of its digits is 12960, while the sum is 36.

The square root of 521618391 is about 22838.9665046385. The cubic root of 521618391 is about 804.9785321487.

The spelling of 521618391 in words is "five hundred twenty-one million, six hundred eighteen thousand, three hundred ninety-one".