81694633661 has 2 divisors, whose sum is σ = 81694633662. Its totient is φ = 81694633660.

The previous prime is 81694633637. The next prime is 81694633663. The reversal of 81694633661 is 16633649618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 68856384025 + 12838249636 = 262405^2 + 113306^2 .

It is a cyclic number.

It is not a de Polignac number, because 81694633661 - 2¹⁰ = 81694632637 is a prime.

It is a Sophie Germain prime.

Together with 81694633663, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81694633663) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40847316830 + 40847316831.

It is an arithmetic number, because the mean of its divisors is an integer number (40847316831).

Almost surely, 2^81694633661 is an apocalyptic number.

It is an amenable number.

81694633661 is a deficient number, since it is larger than the sum of its proper divisors (1).

81694633661 is an equidigital number, since it uses as much as digits as its factorization.

81694633661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3359232, while the sum is 53.

The spelling of 81694633661 in words is "eighty-one billion, six hundred ninety-four million, six hundred thirty-three thousand, six hundred sixty-one".