81312551 has 2 divisors, whose sum is σ = 81312552. Its totient is φ = 81312550.

The previous prime is 81312503. The next prime is 81312557. The reversal of 81312551 is 15521318.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81312551 is a prime.

It is a super-2 number, since 2×81312551² = 13223461900255202, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 81312551.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81312557) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40656275 + 40656276.

It is an arithmetic number, because the mean of its divisors is an integer number (40656276).

Almost surely, 2^81312551 is an apocalyptic number.

81312551 is a deficient number, since it is larger than the sum of its proper divisors (1).

81312551 is an equidigital number, since it uses as much as digits as its factorization.

81312551 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1200, while the sum is 26.

The square root of 81312551 is about 9017.3472263188. The cubic root of 81312551 is about 433.2306710777.

Adding to 81312551 its reverse (15521318), we get a palindrome (96833869).

The spelling of 81312551 in words is "eighty-one million, three hundred twelve thousand, five hundred fifty-one".