81861380 has 48 divisors (see below), whose sum is σ = 175633920. Its totient is φ = 32043648.

The previous prime is 81861349. The next prime is 81861389. The reversal of 81861380 is 8316818.

81861380 = T₁ + T₂ + ... + T₇₈₈.

It is a happy number.

81861380 is a nontrivial binomial coefficient, being equal to C(790, 3).

It is a self number, because there is not a number n which added to its sum of digits gives 81861380.

It is not an unprimeable number, because it can be changed into a prime (81861389) by changing a digit.

It is the 788-th tetrahedral number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 311129 + ... + 311391.

It is an arithmetic number, because the mean of its divisors is an integer number (3659040).

Almost surely, 2^81861380 is an apocalyptic number.

It is an amenable number.

81861380 is an abundant number, since it is smaller than the sum of its proper divisors (93772540).

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

81861380 is a wasteful number, since it uses less digits than its factorization.

81861380 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 548 (or 546 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 35.

The square root of 81861380 is about 9047.7278915759. The cubic root of 81861380 is about 434.2032007322.

The spelling of 81861380 in words is "eighty-one million, eight hundred sixty-one thousand, three hundred eighty".