661187715091 has 2 divisors, whose sum is σ = 661187715092. Its totient is φ = 661187715090.

The previous prime is 661187715073. The next prime is 661187715127. The reversal of 661187715091 is 190517781166.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 661187715091 - 2²⁵ = 661154160659 is a prime.

It is the 813135-th Hogben number.

It is not a weakly prime, because it can be changed into another prime (661187715191) by changing a digit.

It is a nontrivial repunit in base 813134.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330593857545 + 330593857546.

It is an arithmetic number, because the mean of its divisors is an integer number (330593857546).

Almost surely, 2^661187715091 is an apocalyptic number.

661187715091 is a deficient number, since it is larger than the sum of its proper divisors (1).

661187715091 is an equidigital number, since it uses as much as digits as its factorization.

661187715091 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 635040, while the sum is 52.

The spelling of 661187715091 in words is "six hundred sixty-one billion, one hundred eighty-seven million, seven hundred fifteen thousand, ninety-one".