21261021531601 has 2 divisors, whose sum is σ = 21261021531602. Its totient is φ = 21261021531600.

The previous prime is 21261021531583. The next prime is 21261021531641. The reversal of 21261021531601 is 10613512016212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10646359791376 + 10614661740225 = 3262876^2 + 3258015^2 .

It is a cyclic number.

It is not a de Polignac number, because 21261021531601 - 2³⁷ = 21123582578129 is a prime.

It is not a weakly prime, because it can be changed into another prime (21261021531641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10630510765800 + 10630510765801.

It is an arithmetic number, because the mean of its divisors is an integer number (10630510765801).

Almost surely, 2^{21261021531601} is an apocalyptic number.

It is an amenable number.

21261021531601 is a deficient number, since it is larger than the sum of its proper divisors (1).

21261021531601 is an equidigital number, since it uses as much as digits as its factorization.

21261021531601 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4320, while the sum is 31.

Adding to 21261021531601 its reverse (10613512016212), we get a palindrome (31874533547813).

The spelling of 21261021531601 in words is "twenty-one trillion, two hundred sixty-one billion, twenty-one million, five hundred thirty-one thousand, six hundred one".