991551581 has 8 divisors (see below), whose sum is σ = 1019692800. Its totient is φ = 963788320.

The previous prime is 991551569. The next prime is 991551593. The reversal of 991551581 is 185155199.

It is an interprime number because it is at equal distance from previous prime (991551569) and next prime (991551593).

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991551581 is a prime.

It is a super-2 number, since 2×991551581² = 1966349075567199122, 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 (991551521) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 89165 + ... + 99666.

It is an arithmetic number, because the mean of its divisors is an integer number (127461600).

Almost surely, 2^991551581 is an apocalyptic number.

It is an amenable number.

991551581 is a deficient number, since it is larger than the sum of its proper divisors (28141219).

991551581 is a wasteful number, since it uses less digits than its factorization.

991551581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 188979.

The product of its digits is 81000, while the sum is 44.

The square root of 991551581 is about 31488.9120326505. The cubic root of 991551581 is about 997.1758922568.

The spelling of 991551581 in words is "nine hundred ninety-one million, five hundred fifty-one thousand, five hundred eighty-one".