81637681 has 2 divisors, whose sum is σ = 81637682. Its totient is φ = 81637680.

The previous prime is 81637669. The next prime is 81637687. The reversal of 81637681 is 18673618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 54169600 + 27468081 = 7360^2 + 5241^2 .

It is a cyclic number.

It is not a de Polignac number, because 81637681 - 2⁹ = 81637169 is a prime.

It is a super-2 number, since 2×81637681² = 13329421918115522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81637687) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40818840 + 40818841.

It is an arithmetic number, because the mean of its divisors is an integer number (40818841).

Almost surely, 2^81637681 is an apocalyptic number.

It is an amenable number.

81637681 is a deficient number, since it is larger than the sum of its proper divisors (1).

81637681 is an equidigital number, since it uses as much as digits as its factorization.

81637681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 48384, while the sum is 40.

The square root of 81637681 is about 9035.3572701914. The cubic root of 81637681 is about 433.8073305778.

The spelling of 81637681 in words is "eighty-one million, six hundred thirty-seven thousand, six hundred eighty-one".