77666621 has 2 divisors, whose sum is σ = 77666622. Its totient is φ = 77666620.

The previous prime is 77666609. The next prime is 77666627. The reversal of 77666621 is 12666677.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 64080025 + 13586596 = 8005^2 + 3686^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-77666621 is a prime.

It is a nialpdrome in base 10.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (77666627) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 38833310 + 38833311.

It is an arithmetic number, because the mean of its divisors is an integer number (38833311).

Almost surely, 2^77666621 is an apocalyptic number.

It is an amenable number.

77666621 is a deficient number, since it is larger than the sum of its proper divisors (1).

77666621 is an equidigital number, since it uses as much as digits as its factorization.

77666621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 127008, while the sum is 41.

The square root of 77666621 is about 8812.8667866932. The cubic root of 77666621 is about 426.6562746357.

It can be divided in two parts, 77666 and 621, that added together give a palindrome (78287).

The spelling of 77666621 in words is "seventy-seven million, six hundred sixty-six thousand, six hundred twenty-one".