21431252551 has 4 divisors (see below), whose sum is σ = 21562732792. Its totient is φ = 21299772312.

The previous prime is 21431252543. The next prime is 21431252567. The reversal of 21431252551 is 15525213412.

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 21431252551 - 2³ = 21431252543 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21431252251) 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, 65739876 + ... + 65740201.

It is an arithmetic number, because the mean of its divisors is an integer number (5390683198).

Almost surely, 2^21431252551 is an apocalyptic number.

21431252551 is a deficient number, since it is larger than the sum of its proper divisors (131480241).

21431252551 is a wasteful number, since it uses less digits than its factorization.

21431252551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 131480240.

The product of its digits is 12000, while the sum is 31.

Adding to 21431252551 its reverse (15525213412), we get a palindrome (36956465963).

The spelling of 21431252551 in words is "twenty-one billion, four hundred thirty-one million, two hundred fifty-two thousand, five hundred fifty-one".