21507887551 has 4 divisors (see below), whose sum is σ = 21521256400. Its totient is φ = 21494518704.

The previous prime is 21507887537. The next prime is 21507887567. The reversal of 21507887551 is 15578870512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21507887551 - 2⁵ = 21507887519 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21507887495 and 21507887504.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21507887851) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6682011 + ... + 6685228.

It is an arithmetic number, because the mean of its divisors is an integer number (5380314100).

Almost surely, 2^21507887551 is an apocalyptic number.

21507887551 is a deficient number, since it is larger than the sum of its proper divisors (13368849).

21507887551 is a wasteful number, since it uses less digits than its factorization.

21507887551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13368848.

The product of its (nonzero) digits is 784000, while the sum is 49.

The spelling of 21507887551 in words is "twenty-one billion, five hundred seven million, eight hundred eighty-seven thousand, five hundred fifty-one".