81531169 has 2 divisors, whose sum is σ = 81531170. Its totient is φ = 81531168.

The previous prime is 81531143. The next prime is 81531173. The reversal of 81531169 is 96113518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 42406144 + 39125025 = 6512^2 + 6255^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81531169 is a prime.

It is a super-2 number, since 2×81531169² = 13294663037013122, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81535169) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40765584 + 40765585.

It is an arithmetic number, because the mean of its divisors is an integer number (40765585).

Almost surely, 2^81531169 is an apocalyptic number.

It is an amenable number.

81531169 is a deficient number, since it is larger than the sum of its proper divisors (1).

81531169 is an equidigital number, since it uses as much as digits as its factorization.

81531169 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 81531169 is about 9029.4611688627. The cubic root of 81531169 is about 433.6185868705.

The spelling of 81531169 in words is "eighty-one million, five hundred thirty-one thousand, one hundred sixty-nine".