81636641 has 2 divisors, whose sum is σ = 81636642. Its totient is φ = 81636640.

The previous prime is 81636629. The next prime is 81636649. The reversal of 81636641 is 14663618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 78411025 + 3225616 = 8855^2 + 1796^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81636641 is a prime.

It is not a weakly prime, because it can be changed into another prime (81636649) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40818320 + 40818321.

It is an arithmetic number, because the mean of its divisors is an integer number (40818321).

Almost surely, 2^81636641 is an apocalyptic number.

It is an amenable number.

81636641 is a deficient number, since it is larger than the sum of its proper divisors (1).

81636641 is an equidigital number, since it uses as much as digits as its factorization.

81636641 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20736, while the sum is 35.

The square root of 81636641 is about 9035.2997183270. The cubic root of 81636641 is about 433.8054884483.

The spelling of 81636641 in words is "eighty-one million, six hundred thirty-six thousand, six hundred forty-one".