21664273421 has 12 divisors (see below), whose sum is σ = 25274790432. Its totient is φ = 18569362812.

The previous prime is 21664273409. The next prime is 21664273427. The reversal of 21664273421 is 12437246612.

It is a happy number.

It is not a de Polignac number, because 21664273421 - 2¹⁸ = 21664011277 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 (21664273427) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 627695 + ... + 661308.

It is an arithmetic number, because the mean of its divisors is an integer number (2106232536).

Almost surely, 2^21664273421 is an apocalyptic number.

It is an amenable number.

21664273421 is a deficient number, since it is larger than the sum of its proper divisors (3610517011).

21664273421 is an frugal number, since it uses more digits than its factorization.

21664273421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1289038 (or 1289010 counting only the distinct ones).

The product of its digits is 96768, while the sum is 38.

The spelling of 21664273421 in words is "twenty-one billion, six hundred sixty-four million, two hundred seventy-three thousand, four hundred twenty-one".