21612231455981 has 2 divisors, whose sum is σ = 21612231455982. Its totient is φ = 21612231455980.

The previous prime is 21612231455959. The next prime is 21612231456007. The reversal of 21612231455981 is 18955413221612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21574492177225 + 37739278756 = 4644835^2 + 194266^2 .

It is a cyclic number.

It is not a de Polignac number, because 21612231455981 - 2²⁶ = 21612164347117 is a prime.

It is a super-2 number, since 2×21612231455981² (a number of 27 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21612231455911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10806115727990 + 10806115727991.

It is an arithmetic number, because the mean of its divisors is an integer number (10806115727991).

Almost surely, 2^{21612231455981} is an apocalyptic number.

It is an amenable number.

21612231455981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21612231455981 is an equidigital number, since it uses as much as digits as its factorization.

21612231455981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1036800, while the sum is 50.

The spelling of 21612231455981 in words is "twenty-one trillion, six hundred twelve billion, two hundred thirty-one million, four hundred fifty-five thousand, nine hundred eighty-one".