81661815 has 24 divisors (see below), whose sum is σ = 143491920. Its totient is φ = 42954624.

The previous prime is 81661813. The next prime is 81661837. The reversal of 81661815 is 51816618.

It is not a de Polignac number, because 81661815 - 2¹ = 81661813 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81661815.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81661813) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 9145 + ... + 15714.

It is an arithmetic number, because the mean of its divisors is an integer number (5978830).

Almost surely, 2^81661815 is an apocalyptic number.

81661815 is a deficient number, since it is larger than the sum of its proper divisors (61830105).

81661815 is a wasteful number, since it uses less digits than its factorization.

81661815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24943 (or 24940 counting only the distinct ones).

The product of its digits is 11520, while the sum is 36.

The square root of 81661815 is about 9036.6927025323. The cubic root of 81661815 is about 433.8500742165.

It can be divided in two parts, 8166 and 1815, that multiplied together give a triangular number (14821290 = T₅₄₄₄).

The spelling of 81661815 in words is "eighty-one million, six hundred sixty-one thousand, eight hundred fifteen".