21551257687 has 2 divisors, whose sum is σ = 21551257688. Its totient is φ = 21551257686.

The previous prime is 21551257657. The next prime is 21551257729. The reversal of 21551257687 is 78675215512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21551257687 - 2²³ = 21542869079 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21551257687.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21551257657) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10775628843 + 10775628844.

It is an arithmetic number, because the mean of its divisors is an integer number (10775628844).

Almost surely, 2^21551257687 is an apocalyptic number.

21551257687 is a deficient number, since it is larger than the sum of its proper divisors (1).

21551257687 is an equidigital number, since it uses as much as digits as its factorization.

21551257687 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1176000, while the sum is 49.

The spelling of 21551257687 in words is "twenty-one billion, five hundred fifty-one million, two hundred fifty-seven thousand, six hundred eighty-seven".