81904661 has 2 divisors, whose sum is σ = 81904662. Its totient is φ = 81904660.

The previous prime is 81904621. The next prime is 81904681. The reversal of 81904661 is 16640918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 77880625 + 4024036 = 8825^2 + 2006^2 .

It is a cyclic number.

It is not a de Polignac number, because 81904661 - 2²² = 77710357 is a prime.

It is a Chen prime.

It is equal to p_4774175 and since 81904661 and 4774175 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81904621) 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, 40952330 + 40952331.

It is an arithmetic number, because the mean of its divisors is an integer number (40952331).

Almost surely, 2^81904661 is an apocalyptic number.

It is an amenable number.

81904661 is a deficient number, since it is larger than the sum of its proper divisors (1).

81904661 is an equidigital number, since it uses as much as digits as its factorization.

81904661 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 10368, while the sum is 35.

The square root of 81904661 is about 9050.1193914777. The cubic root of 81904661 is about 434.2797098981.

The spelling of 81904661 in words is "eighty-one million, nine hundred four thousand, six hundred sixty-one".