81311779 has 2 divisors, whose sum is σ = 81311780. Its totient is φ = 81311778.

The previous prime is 81311743. The next prime is 81311801. The reversal of 81311779 is 97711318.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81311779 - 2²³ = 72923171 is a prime.

It is a super-2 number, since 2×81311779² = 13223210808289682, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81311179) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40655889 + 40655890.

It is an arithmetic number, because the mean of its divisors is an integer number (40655890).

Almost surely, 2^81311779 is an apocalyptic number.

81311779 is a deficient number, since it is larger than the sum of its proper divisors (1).

81311779 is an equidigital number, since it uses as much as digits as its factorization.

81311779 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10584, while the sum is 37.

The square root of 81311779 is about 9017.3044198363. The cubic root of 81311779 is about 433.2293000096.

The spelling of 81311779 in words is "eighty-one million, three hundred eleven thousand, seven hundred seventy-nine".