9721250121581 has 2 divisors, whose sum is σ = 9721250121582. Its totient is φ = 9721250121580.

The previous prime is 9721250121547. The next prime is 9721250121607. The reversal of 9721250121581 is 1851210521279.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 8756071592356 + 965178529225 = 2959066^2 + 982435^2 .

It is a cyclic number.

It is not a de Polignac number, because 9721250121581 - 2¹⁴ = 9721250105197 is a prime.

It is a super-2 number, since 2×9721250121581² (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 (9721250121511) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4860625060790 + 4860625060791.

It is an arithmetic number, because the mean of its divisors is an integer number (4860625060791).

Almost surely, 2^{9721250121581} is an apocalyptic number.

It is an amenable number.

9721250121581 is a deficient number, since it is larger than the sum of its proper divisors (1).

9721250121581 is an equidigital number, since it uses as much as digits as its factorization.

9721250121581 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 100800, while the sum is 44.

The spelling of 9721250121581 in words is "nine trillion, seven hundred twenty-one billion, two hundred fifty million, one hundred twenty-one thousand, five hundred eighty-one".