21387802746581 has 2 divisors, whose sum is σ = 21387802746582. Its totient is φ = 21387802746580.

The previous prime is 21387802746559. The next prime is 21387802746587. The reversal of 21387802746581 is 18564720878312.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20383337773681 + 1004464972900 = 4514791^2 + 1002230^2 .

It is a cyclic number.

It is not a de Polignac number, because 21387802746581 - 2¹⁴ = 21387802730197 is a prime.

It is a super-2 number, since 2×21387802746581² (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 (21387802746587) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10693901373290 + 10693901373291.

It is an arithmetic number, because the mean of its divisors is an integer number (10693901373291).

Almost surely, 2^{21387802746581} is an apocalyptic number.

It is an amenable number.

21387802746581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21387802746581 is an equidigital number, since it uses as much as digits as its factorization.

21387802746581 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 36126720, while the sum is 62.

The spelling of 21387802746581 in words is "twenty-one trillion, three hundred eighty-seven billion, eight hundred two million, seven hundred forty-six thousand, five hundred eighty-one".