21557677777 has 2 divisors, whose sum is σ = 21557677778. Its totient is φ = 21557677776.

The previous prime is 21557677753. The next prime is 21557677787. The reversal of 21557677777 is 77777675512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14768082576 + 6789595201 = 121524^2 + 82399^2 .

It is a cyclic number.

It is not a de Polignac number, because 21557677777 - 2⁷ = 21557677649 is a prime.

It is a super-2 number, since 2×21557677777² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21557677787) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778838888 + 10778838889.

It is an arithmetic number, because the mean of its divisors is an integer number (10778838889).

Almost surely, 2^21557677777 is an apocalyptic number.

It is an amenable number.

21557677777 is a deficient number, since it is larger than the sum of its proper divisors (1).

21557677777 is an equidigital number, since it uses as much as digits as its factorization.

21557677777 is an evil number, because the sum of its binary digits is even.

The product of its digits is 35294700, while the sum is 61.

The spelling of 21557677777 in words is "twenty-one billion, five hundred fifty-seven million, six hundred seventy-seven thousand, seven hundred seventy-seven".