15631981 has 2 divisors, whose sum is σ = 15631982. Its totient is φ = 15631980.

The previous prime is 15631961. The next prime is 15631997. The reversal of 15631981 is 18913651.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15093225 + 538756 = 3885^2 + 734^2 .

It is a cyclic number.

It is not a de Polignac number, because 15631981 - 2⁵ = 15631949 is a prime.

It is a super-2 number, since 2×15631981² = 488717659968722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (15631961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7815990 + 7815991.

It is an arithmetic number, because the mean of its divisors is an integer number (7815991).

Almost surely, 2^15631981 is an apocalyptic number.

It is an amenable number.

15631981 is a deficient number, since it is larger than the sum of its proper divisors (1).

15631981 is an equidigital number, since it uses as much as digits as its factorization.

15631981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6480, while the sum is 34.

The square root of 15631981 is about 3953.7300110149. The cubic root of 15631981 is about 250.0372264565.

The spelling of 15631981 in words is "fifteen million, six hundred thirty-one thousand, nine hundred eighty-one".