81615919 has 24 divisors (see below), whose sum is σ = 105563088. Its totient is φ = 62375040.

The previous prime is 81615907. The next prime is 81615943. The reversal of 81615919 is 91951618.

It is a de Polignac number, because none of the positive numbers 2^k-81615919 is a prime.

It is a super-2 number, since 2×81615919² = 13322316468429122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81615949) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 27139 + ... + 29995.

It is an arithmetic number, because the mean of its divisors is an integer number (4398462).

Almost surely, 2^81615919 is an apocalyptic number.

81615919 is the 5714-th heptagonal number.

81615919 is a deficient number, since it is larger than the sum of its proper divisors (23947169).

81615919 is a wasteful number, since it uses less digits than its factorization.

81615919 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2935 (or 2928 counting only the distinct ones).

The product of its digits is 19440, while the sum is 40.

The square root of 81615919 is about 9034.1529209993. The cubic root of 81615919 is about 433.7687807563.

The spelling of 81615919 in words is "eighty-one million, six hundred fifteen thousand, nine hundred nineteen".