15681661 has 2 divisors, whose sum is σ = 15681662. Its totient is φ = 15681660.

The previous prime is 15681649. The next prime is 15681671. The reversal of 15681661 is 16618651.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13461561 + 2220100 = 3669^2 + 1490^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-15681661 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (15681671) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7840830 + 7840831.

It is an arithmetic number, because the mean of its divisors is an integer number (7840831).

Almost surely, 2^15681661 is an apocalyptic number.

It is an amenable number.

15681661 is a deficient number, since it is larger than the sum of its proper divisors (1).

15681661 is an equidigital number, since it uses as much as digits as its factorization.

15681661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8640, while the sum is 34.

The square root of 15681661 is about 3960.0077020127. The cubic root of 15681661 is about 250.3018274541.

The spelling of 15681661 in words is "fifteen million, six hundred eighty-one thousand, six hundred sixty-one".