21156957281 has 4 divisors (see below), whose sum is σ = 21180810432. Its totient is φ = 21133104132.

The previous prime is 21156957257. The next prime is 21156957293. The reversal of 21156957281 is 18275965112.

It is a happy number.

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 a cyclic number.

It is not a de Polignac number, because 21156957281 - 2¹⁰ = 21156956257 is a prime.

It is a super-2 number, since 2×21156957281² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21156957251) 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, 11925245 + ... + 11927018.

It is an arithmetic number, because the mean of its divisors is an integer number (5295202608).

Almost surely, 2^21156957281 is an apocalyptic number.

It is an amenable number.

21156957281 is a deficient number, since it is larger than the sum of its proper divisors (23853151).

21156957281 is an equidigital number, since it uses as much as digits as its factorization.

21156957281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23853150.

The product of its digits is 302400, while the sum is 47.

The spelling of 21156957281 in words is "twenty-one billion, one hundred fifty-six million, nine hundred fifty-seven thousand, two hundred eighty-one".