91581997 has 4 divisors (see below), whose sum is σ = 98626780. Its totient is φ = 84537216.

The previous prime is 91581947. The next prime is 91582013. The reversal of 91581997 is 79918519.

It is a happy number.

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 36614601 + 54967396 = 6051^2 + 7414^2 .

It is a cyclic number.

It is not a de Polignac number, because 91581997 - 2¹¹ = 91579949 is a prime.

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 91581997.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (91581937) 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, 3522372 + ... + 3522397.

It is an arithmetic number, because the mean of its divisors is an integer number (24656695).

Almost surely, 2^91581997 is an apocalyptic number.

It is an amenable number.

91581997 is a deficient number, since it is larger than the sum of its proper divisors (7044783).

91581997 is a wasteful number, since it uses less digits than its factorization.

91581997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7044782.

The product of its digits is 204120, while the sum is 49.

The square root of 91581997 is about 9569.8483269068. The cubic root of 91581997 is about 450.7510043888.

The spelling of 91581997 in words is "ninety-one million, five hundred eighty-one thousand, nine hundred ninety-seven".