81311987 has 2 divisors, whose sum is σ = 81311988. Its totient is φ = 81311986.

The previous prime is 81311957. The next prime is 81312013. The reversal of 81311987 is 78911318.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81311987 - 2¹⁰ = 81310963 is a prime.

It is a super-2 number, since 2×81311987² = 13223278459776338, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81311987.

It is not a weakly prime, because it can be changed into another prime (81311917) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40655993 + 40655994.

It is an arithmetic number, because the mean of its divisors is an integer number (40655994).

Almost surely, 2^81311987 is an apocalyptic number.

81311987 is a deficient number, since it is larger than the sum of its proper divisors (1).

81311987 is an equidigital number, since it uses as much as digits as its factorization.

81311987 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 12096, while the sum is 38.

The square root of 81311987 is about 9017.3159532091. The cubic root of 81311987 is about 433.2296694174.

The spelling of 81311987 in words is "eighty-one million, three hundred eleven thousand, nine hundred eighty-seven".