661773817 has 2 divisors, whose sum is σ = 661773818. Its totient is φ = 661773816.

The previous prime is 661773797. The next prime is 661773869. The reversal of 661773817 is 718377166.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 645363216 + 16410601 = 25404^2 + 4051^2 .

It is a cyclic number.

It is not a de Polignac number, because 661773817 - 2²⁷ = 527556089 is a prime.

It is not a weakly prime, because it can be changed into another prime (661773877) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330886908 + 330886909.

It is an arithmetic number, because the mean of its divisors is an integer number (330886909).

Almost surely, 2^661773817 is an apocalyptic number.

It is an amenable number.

661773817 is a deficient number, since it is larger than the sum of its proper divisors (1).

661773817 is an equidigital number, since it uses as much as digits as its factorization.

661773817 is an evil number, because the sum of its binary digits is even.

The product of its digits is 296352, while the sum is 46.

The square root of 661773817 is about 25724.9648590625. The cubic root of 661773817 is about 871.4380659963.

The spelling of 661773817 in words is "six hundred sixty-one million, seven hundred seventy-three thousand, eight hundred seventeen".