81512009 has 2 divisors, whose sum is σ = 81512010. Its totient is φ = 81512008.

The previous prime is 81511993. The next prime is 81512117. The reversal of 81512009 is 90021518.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 81504784 + 7225 = 9028^2 + 85^2 .

It is a cyclic number.

It is not a de Polignac number, because 81512009 - 2⁴ = 81511993 is a prime.

It is a super-2 number, since 2×81512009² = 13288415222432162, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (81512309) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40756004 + 40756005.

It is an arithmetic number, because the mean of its divisors is an integer number (40756005).

Almost surely, 2^81512009 is an apocalyptic number.

It is an amenable number.

81512009 is a deficient number, since it is larger than the sum of its proper divisors (1).

81512009 is an equidigital number, since it uses as much as digits as its factorization.

81512009 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 720, while the sum is 26.

The square root of 81512009 is about 9028.4001351291. The cubic root of 81512009 is about 433.5846171094.

The spelling of 81512009 in words is "eighty-one million, five hundred twelve thousand, nine".