1681957661 has 2 divisors, whose sum is σ = 1681957662. Its totient is φ = 1681957660.

The previous prime is 1681957649. The next prime is 1681957763. The reversal of 1681957661 is 1667591861.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1518271225 + 163686436 = 38965^2 + 12794^2 .

It is a cyclic number.

It is not a de Polignac number, because 1681957661 - 2²² = 1677763357 is a prime.

It is a Sophie Germain 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 (1681957261) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 840978830 + 840978831.

It is an arithmetic number, because the mean of its divisors is an integer number (840978831).

Almost surely, 2^1681957661 is an apocalyptic number.

It is an amenable number.

1681957661 is a deficient number, since it is larger than the sum of its proper divisors (1).

1681957661 is an equidigital number, since it uses as much as digits as its factorization.

1681957661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 544320, while the sum is 50.

The square root of 1681957661 is about 41011.6771298127. The cubic root of 1681957661 is about 1189.2459646532.

The spelling of 1681957661 in words is "one billion, six hundred eighty-one million, nine hundred fifty-seven thousand, six hundred sixty-one".