81531390 has 16 divisors (see below), whose sum is σ = 195675408. Its totient is φ = 21741696.

The previous prime is 81531379. The next prime is 81531391. The reversal of 81531390 is 9313518.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (30), and also a Moran number because the ratio is a prime number: 2717713 = 81531390 / (8 + 1 + 5 + 3 + 1 + 3 + 9 + 0).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81531391) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1358827 + ... + 1358886.

It is an arithmetic number, because the mean of its divisors is an integer number (12229713).

Almost surely, 2^81531390 is an apocalyptic number.

81531390 is an abundant number, since it is smaller than the sum of its proper divisors (114144018).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81531390 is a wasteful number, since it uses less digits than its factorization.

81531390 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2717723.

The product of its (nonzero) digits is 3240, while the sum is 30.

The square root of 81531390 is about 9029.4734065725. The cubic root of 81531390 is about 433.6189786619.

The spelling of 81531390 in words is "eighty-one million, five hundred thirty-one thousand, three hundred ninety".