81615554 has 4 divisors (see below), whose sum is σ = 122423334. Its totient is φ = 40807776.

The previous prime is 81615553. The next prime is 81615563. The reversal of 81615554 is 45551618.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 75290329 + 6325225 = 8677^2 + 2515^2 .

It is a super-2 number, since 2×81615554² = 13322197309453832, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81615551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20403887 + ... + 20403890.

Almost surely, 2^81615554 is an apocalyptic number.

81615554 is a deficient number, since it is larger than the sum of its proper divisors (40807780).

81615554 is a wasteful number, since it uses less digits than its factorization.

81615554 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40807779.

The product of its digits is 24000, while the sum is 35.

The square root of 81615554 is about 9034.1327198575. The cubic root of 81615554 is about 433.7681341266.

The spelling of 81615554 in words is "eighty-one million, six hundred fifteen thousand, five hundred fifty-four".