87991805 has 12 divisors (see below), whose sum is σ = 116062716. Its totient is φ = 63993600.

The previous prime is 87991769. The next prime is 87991807. The reversal of 87991805 is 50819978.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 10745284 + 77246521 = 3278^2 + 8789^2 .

It is not a de Polignac number, because 87991805 - 2⁶ = 87991741 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 87991805.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (87991807) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 72116 + ... + 73325.

It is an arithmetic number, because the mean of its divisors is an integer number (9671893).

Almost surely, 2^87991805 is an apocalyptic number.

It is an amenable number.

87991805 is a deficient number, since it is larger than the sum of its proper divisors (28070911).

87991805 is a wasteful number, since it uses less digits than its factorization.

87991805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 145468 (or 145457 counting only the distinct ones).

The product of its (nonzero) digits is 181440, while the sum is 47.

The square root of 87991805 is about 9380.3947145096. The cubic root of 87991805 is about 444.7822104755.

The spelling of 87991805 in words is "eighty-seven million, nine hundred ninety-one thousand, eight hundred five".