21615842981 has 2 divisors, whose sum is σ = 21615842982. Its totient is φ = 21615842980.

The previous prime is 21615842977. The next prime is 21615842987. The reversal of 21615842981 is 18924851612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15217442881 + 6398400100 = 123359^2 + 79990^2 .

It is a cyclic number.

It is not a de Polignac number, because 21615842981 - 2² = 21615842977 is a prime.

It is a super-2 number, since 2×21615842981² (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 (21615842987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10807921490 + 10807921491.

It is an arithmetic number, because the mean of its divisors is an integer number (10807921491).

Almost surely, 2^21615842981 is an apocalyptic number.

It is an amenable number.

21615842981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21615842981 is an equidigital number, since it uses as much as digits as its factorization.

21615842981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 276480, while the sum is 47.

The spelling of 21615842981 in words is "twenty-one billion, six hundred fifteen million, eight hundred forty-two thousand, nine hundred eighty-one".