81977921 has 2 divisors, whose sum is σ = 81977922. Its totient is φ = 81977920.

The previous prime is 81977897. The next prime is 81977933. The reversal of 81977921 is 12977918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 67240000 + 14737921 = 8200^2 + 3839^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81977921 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81977941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40988960 + 40988961.

It is an arithmetic number, because the mean of its divisors is an integer number (40988961).

Almost surely, 2^81977921 is an apocalyptic number.

It is an amenable number.

81977921 is a deficient number, since it is larger than the sum of its proper divisors (1).

81977921 is an equidigital number, since it uses as much as digits as its factorization.

81977921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 63504, while the sum is 44.

The square root of 81977921 is about 9054.1659472311. The cubic root of 81977921 is about 434.4091524723.

The spelling of 81977921 in words is "eighty-one million, nine hundred seventy-seven thousand, nine hundred twenty-one".