81612991 has 2 divisors, whose sum is σ = 81612992. Its totient is φ = 81612990.

The previous prime is 81612983. The next prime is 81612997. The reversal of 81612991 is 19921618.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81612991 - 2³ = 81612983 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81612991.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81612997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40806495 + 40806496.

It is an arithmetic number, because the mean of its divisors is an integer number (40806496).

Almost surely, 2^81612991 is an apocalyptic number.

81612991 is a deficient number, since it is larger than the sum of its proper divisors (1).

81612991 is an equidigital number, since it uses as much as digits as its factorization.

81612991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7776, while the sum is 37.

The square root of 81612991 is about 9033.9908678280. The cubic root of 81612991 is about 433.7635934914.

The spelling of 81612991 in words is "eighty-one million, six hundred twelve thousand, nine hundred ninety-one".