21640512421 has 4 divisors (see below), whose sum is σ = 23607831744. Its totient is φ = 19673193100.

The previous prime is 21640512407. The next prime is 21640512497. The reversal of 21640512421 is 12421504612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21640512421 - 2¹¹ = 21640510373 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21640512421.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21640512401) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 983659645 + ... + 983659666.

It is an arithmetic number, because the mean of its divisors is an integer number (5901957936).

Almost surely, 2^21640512421 is an apocalyptic number.

It is an amenable number.

21640512421 is a deficient number, since it is larger than the sum of its proper divisors (1967319323).

21640512421 is a wasteful number, since it uses less digits than its factorization.

21640512421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1967319322.

The product of its (nonzero) digits is 3840, while the sum is 28.

It can be divided in two parts, 216405 and 12421, that added together give a triangular number (228826 = T₆₇₆).

The spelling of 21640512421 in words is "twenty-one billion, six hundred forty million, five hundred twelve thousand, four hundred twenty-one".