991551481 has 4 divisors (see below), whose sum is σ = 1005134452. Its totient is φ = 977968512.

The previous prime is 991551443. The next prime is 991551487. The reversal of 991551481 is 184155199.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 184155199 = 397 ⋅463867.

It can be written as a sum of positive squares in 2 ways, for example, as 359481600 + 632069881 = 18960^2 + 25141^2 .

It is a cyclic number.

It is not a de Polignac number, because 991551481 - 2¹⁵ = 991518713 is a prime.

It is a super-2 number, since 2×991551481² = 1966348678946586722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991551487) 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, 6791376 + ... + 6791521.

It is an arithmetic number, because the mean of its divisors is an integer number (251283613).

Almost surely, 2^991551481 is an apocalyptic number.

It is an amenable number.

991551481 is a deficient number, since it is larger than the sum of its proper divisors (13582971).

991551481 is a wasteful number, since it uses less digits than its factorization.

991551481 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13582970.

The product of its digits is 64800, while the sum is 43.

The square root of 991551481 is about 31488.9104447899. The cubic root of 991551481 is about 997.1758587343.

The spelling of 991551481 in words is "nine hundred ninety-one million, five hundred fifty-one thousand, four hundred eighty-one".