21581358157561 has 2 divisors, whose sum is σ = 21581358157562. Its totient is φ = 21581358157560.

The previous prime is 21581358157547. The next prime is 21581358157637. The reversal of 21581358157561 is 16575185318512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14610596509161 + 6970761648400 = 3822381^2 + 2640220^2 .

It is a cyclic number.

It is not a de Polignac number, because 21581358157561 - 2⁵ = 21581358157529 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21581358157496 and 21581358157505.

It is not a weakly prime, because it can be changed into another prime (21581358157531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10790679078780 + 10790679078781.

It is an arithmetic number, because the mean of its divisors is an integer number (10790679078781).

Almost surely, 2^{21581358157561} is an apocalyptic number.

It is an amenable number.

21581358157561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21581358157561 is an equidigital number, since it uses as much as digits as its factorization.

21581358157561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10080000, while the sum is 58.

The spelling of 21581358157561 in words is "twenty-one trillion, five hundred eighty-one billion, three hundred fifty-eight million, one hundred fifty-seven thousand, five hundred sixty-one".