81638775 has 36 divisors (see below), whose sum is σ = 147427072. Its totient is φ = 43182720.

The previous prime is 81638759. The next prime is 81638803. The reversal of 81638775 is 57783618.

81638775 is a `hidden beast` number, since 8 + 1 + 638 + 7 + 7 + 5 = 666.

It is not a de Polignac number, because 81638775 - 2⁴ = 81638759 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81638775.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 27147 + ... + 30003.

Almost surely, 2^81638775 is an apocalyptic number.

81638775 is a deficient number, since it is larger than the sum of its proper divisors (65788297).

81638775 is a wasteful number, since it uses less digits than its factorization.

81638775 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3000 (or 2992 counting only the distinct ones).

The product of its digits is 282240, while the sum is 45.

The square root of 81638775 is about 9035.4178099300. The cubic root of 81638775 is about 433.8092683395.

The spelling of 81638775 in words is "eighty-one million, six hundred thirty-eight thousand, seven hundred seventy-five".