81391642 has 16 divisors (see below), whose sum is σ = 126787752. Its totient is φ = 39156480.

The previous prime is 81391619. The next prime is 81391669. The reversal of 81391642 is 24619318.

It can be written as a sum of positive squares in 4 ways, for example, as 32936121 + 48455521 = 5739^2 + 6961^2 .

It is a junction number, because it is equal to n+sod(n) for n = 81391598 and 81391607.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 813 + ... + 12784.

Almost surely, 2^81391642 is an apocalyptic number.

81391642 is a gapful number since it is divisible by the number (82) formed by its first and last digit.

81391642 is a deficient number, since it is larger than the sum of its proper divisors (45396110).

81391642 is a wasteful number, since it uses less digits than its factorization.

81391642 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13713.

The product of its digits is 10368, while the sum is 34.

The square root of 81391642 is about 9021.7316519613. The cubic root of 81391642 is about 433.3710903327.

The spelling of 81391642 in words is "eighty-one million, three hundred ninety-one thousand, six hundred forty-two".