21157607761 has 2 divisors, whose sum is σ = 21157607762. Its totient is φ = 21157607760.

The previous prime is 21157607759. The next prime is 21157607767. The reversal of 21157607761 is 16770675112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19423718161 + 1733889600 = 139369^2 + 41640^2 .

It is a cyclic number.

It is not a de Polignac number, because 21157607761 - 2¹ = 21157607759 is a prime.

Together with 21157607759, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21157607767) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10578803880 + 10578803881.

It is an arithmetic number, because the mean of its divisors is an integer number (10578803881).

Almost surely, 2^21157607761 is an apocalyptic number.

It is an amenable number.

21157607761 is a deficient number, since it is larger than the sum of its proper divisors (1).

21157607761 is an equidigital number, since it uses as much as digits as its factorization.

21157607761 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 123480, while the sum is 43.

The spelling of 21157607761 in words is "twenty-one billion, one hundred fifty-seven million, six hundred seven thousand, seven hundred sixty-one".