81990731 has 2 divisors, whose sum is σ = 81990732. Its totient is φ = 81990730.

The previous prime is 81990709. The next prime is 81990751. The reversal of 81990731 is 13709918.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81990731 - 2¹⁰ = 81989707 is a prime.

It is a super-2 number, since 2×81990731² = 13444959939828722, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81990751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40995365 + 40995366.

It is an arithmetic number, because the mean of its divisors is an integer number (40995366).

Almost surely, 2^81990731 is an apocalyptic number.

81990731 is a deficient number, since it is larger than the sum of its proper divisors (1).

81990731 is an equidigital number, since it uses as much as digits as its factorization.

81990731 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 13608, while the sum is 38.

The square root of 81990731 is about 9054.8733287661. The cubic root of 81990731 is about 434.4317784483.

The spelling of 81990731 in words is "eighty-one million, nine hundred ninety thousand, seven hundred thirty-one".