21391765542 has 24 divisors (see below), whose sum is σ = 52970086416. Its totient is φ = 6111932976.

The previous prime is 21391765537. The next prime is 21391765579. The reversal of 21391765542 is 24556719312.

21391765542 is a `hidden beast` number, since 2 + 1 + 3 + 91 + 7 + 6 + 554 + 2 = 666.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 84887833 + ... + 84888084.

It is an arithmetic number, because the mean of its divisors is an integer number (2207086934).

Almost surely, 2^21391765542 is an apocalyptic number.

21391765542 is an abundant number, since it is smaller than the sum of its proper divisors (31578320874).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21391765542 is a wasteful number, since it uses less digits than its factorization.

21391765542 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 169775932 (or 169775929 counting only the distinct ones).

The product of its digits is 453600, while the sum is 45.

The spelling of 21391765542 in words is "twenty-one billion, three hundred ninety-one million, seven hundred sixty-five thousand, five hundred forty-two".