90991991 has 8 divisors (see below), whose sum is σ = 93709824. Its totient is φ = 88287840.

The previous prime is 90991961. The next prime is 90992017. The reversal of 90991991 is 19919909.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 90991991 - 2²² = 86797687 is a prime.

It is a super-2 number, since 2×90991991² = 16559084852288162, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (90991961) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10961 + ... + 17381.

It is an arithmetic number, because the mean of its divisors is an integer number (11713728).

Almost surely, 2^90991991 is an apocalyptic number.

90991991 is a deficient number, since it is larger than the sum of its proper divisors (2717833).

90991991 is a wasteful number, since it uses less digits than its factorization.

90991991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6841.

The product of its (nonzero) digits is 59049, while the sum is 47.

The square root of 90991991 is about 9538.9722192697. The cubic root of 90991991 is about 449.7809485312.

The spelling of 90991991 in words is "ninety million, nine hundred ninety-one thousand, nine hundred ninety-one".