21454331981 has 2 divisors, whose sum is σ = 21454331982. Its totient is φ = 21454331980.

The previous prime is 21454331953. The next prime is 21454332013. The reversal of 21454331981 is 18913345412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20698576900 + 755755081 = 143870^2 + 27491^2 .

It is a cyclic number.

It is not a de Polignac number, because 21454331981 - 2⁶ = 21454331917 is a prime.

It is a super-2 number, since 2×21454331981² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21454331911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10727165990 + 10727165991.

It is an arithmetic number, because the mean of its divisors is an integer number (10727165991).

Almost surely, 2^21454331981 is an apocalyptic number.

It is an amenable number.

21454331981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21454331981 is an equidigital number, since it uses as much as digits as its factorization.

21454331981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 103680, while the sum is 41.

The spelling of 21454331981 in words is "twenty-one billion, four hundred fifty-four million, three hundred thirty-one thousand, nine hundred eighty-one".