21657812981 has 16 divisors (see below), whose sum is σ = 25488304128. Its totient is φ = 18016195200.

The previous prime is 21657812947. The next prime is 21657813007. The reversal of 21657812981 is 18921875612.

It is a cyclic number.

It is not a de Polignac number, because 21657812981 - 2²⁶ = 21590704117 is a prime.

It is a super-2 number, since 2×21657812981² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21657812941) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 142730 + ... + 252363.

It is an arithmetic number, because the mean of its divisors is an integer number (1593019008).

Almost surely, 2^21657812981 is an apocalyptic number.

It is an amenable number.

21657812981 is a deficient number, since it is larger than the sum of its proper divisors (3830491147).

21657812981 is a wasteful number, since it uses less digits than its factorization.

21657812981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 395332.

The product of its digits is 483840, while the sum is 50.

The spelling of 21657812981 in words is "twenty-one billion, six hundred fifty-seven million, eight hundred twelve thousand, nine hundred eighty-one".