661565137 has 2 divisors, whose sum is σ = 661565138. Its totient is φ = 661565136.

The previous prime is 661565119. The next prime is 661565147. The reversal of 661565137 is 731565166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 624550081 + 37015056 = 24991^2 + 6084^2 .

It is a cyclic number.

It is not a de Polignac number, because 661565137 - 2²⁷ = 527347409 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 661565137.

It is not a weakly prime, because it can be changed into another prime (661565147) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330782568 + 330782569.

It is an arithmetic number, because the mean of its divisors is an integer number (330782569).

Almost surely, 2^661565137 is an apocalyptic number.

It is an amenable number.

661565137 is a deficient number, since it is larger than the sum of its proper divisors (1).

661565137 is an equidigital number, since it uses as much as digits as its factorization.

661565137 is an evil number, because the sum of its binary digits is even.

The product of its digits is 113400, while the sum is 40.

The square root of 661565137 is about 25720.9085570475. The cubic root of 661565137 is about 871.3464582551.

The spelling of 661565137 in words is "six hundred sixty-one million, five hundred sixty-five thousand, one hundred thirty-seven".