81961657 has 2 divisors, whose sum is σ = 81961658. Its totient is φ = 81961656.

The previous prime is 81961639. The next prime is 81961661. The reversal of 81961657 is 75616918.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 59151481 + 22810176 = 7691^2 + 4776^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81961657 is a prime.

It is not a weakly prime, because it can be changed into another prime (81961637) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40980828 + 40980829.

It is an arithmetic number, because the mean of its divisors is an integer number (40980829).

Almost surely, 2^81961657 is an apocalyptic number.

It is an amenable number.

81961657 is a deficient number, since it is larger than the sum of its proper divisors (1).

81961657 is an equidigital number, since it uses as much as digits as its factorization.

81961657 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 90720, while the sum is 43.

The square root of 81961657 is about 9053.2677525853. The cubic root of 81961657 is about 434.3804223880.

The spelling of 81961657 in words is "eighty-one million, nine hundred sixty-one thousand, six hundred fifty-seven".