77778661 has 2 divisors, whose sum is σ = 77778662. Its totient is φ = 77778660.

The previous prime is 77778641. The next prime is 77778671. The reversal of 77778661 is 16687777.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 74909025 + 2869636 = 8655^2 + 1694^2 .

It is a cyclic number.

It is not a de Polignac number, because 77778661 - 2⁵ = 77778629 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (77778641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 38889330 + 38889331.

It is an arithmetic number, because the mean of its divisors is an integer number (38889331).

Almost surely, 2^77778661 is an apocalyptic number.

It is an amenable number.

77778661 is a deficient number, since it is larger than the sum of its proper divisors (1).

77778661 is an equidigital number, since it uses as much as digits as its factorization.

77778661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 691488, while the sum is 49.

The square root of 77778661 is about 8819.2211107331. The cubic root of 77778661 is about 426.8613374221.

The spelling of 77778661 in words is "seventy-seven million, seven hundred seventy-eight thousand, six hundred sixty-one".