90391981 has 4 divisors (see below), whose sum is σ = 90914652. Its totient is φ = 89869312.

The previous prime is 90391979. The next prime is 90391991. The reversal of 90391981 is 18919309.

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

It can be written as a sum of positive squares in 2 ways, for example, as 48024900 + 42367081 = 6930^2 + 6509^2 .

It is a cyclic number.

It is not a de Polignac number, because 90391981 - 2¹ = 90391979 is a prime.

It is a super-2 number, since 2×90391981² = 16341420458208722, which contains 22 as substring.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (90391991) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 261076 + ... + 261421.

It is an arithmetic number, because the mean of its divisors is an integer number (22728663).

Almost surely, 2^90391981 is an apocalyptic number.

It is an amenable number.

90391981 is a deficient number, since it is larger than the sum of its proper divisors (522671).

90391981 is a wasteful number, since it uses less digits than its factorization.

90391981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 522670.

The product of its (nonzero) digits is 17496, while the sum is 40.

The square root of 90391981 is about 9507.4697475196. The cubic root of 90391981 is about 448.7901344447.

The spelling of 90391981 in words is "ninety million, three hundred ninety-one thousand, nine hundred eighty-one".