81987775 has 6 divisors (see below), whose sum is σ = 101664872. Its totient is φ = 65590200.

The previous prime is 81987769. The next prime is 81987781. The reversal of 81987775 is 57778918.

It is an interprime number because it is at equal distance from previous prime (81987769) and next prime (81987781).

It is not a de Polignac number, because 81987775 - 2¹⁷ = 81856703 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1639731 + ... + 1639780.

Almost surely, 2^81987775 is an apocalyptic number.

81987775 is a deficient number, since it is larger than the sum of its proper divisors (19677097).

81987775 is a wasteful number, since it uses less digits than its factorization.

81987775 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3279521 (or 3279516 counting only the distinct ones).

The product of its digits is 987840, while the sum is 52.

The square root of 81987775 is about 9054.7101002738. The cubic root of 81987775 is about 434.4265575501.

The spelling of 81987775 in words is "eighty-one million, nine hundred eighty-seven thousand, seven hundred seventy-five".