18915581 has 2 divisors, whose sum is σ = 18915582. Its totient is φ = 18915580.

The previous prime is 18915553. The next prime is 18915599. The reversal of 18915581 is 18551981.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18567481 + 348100 = 4309^2 + 590^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18915581 is a prime.

It is a super-2 number, since 2×18915581² = 715598409135122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18915521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9457790 + 9457791.

It is an arithmetic number, because the mean of its divisors is an integer number (9457791).

Almost surely, 2^18915581 is an apocalyptic number.

It is an amenable number.

18915581 is a deficient number, since it is larger than the sum of its proper divisors (1).

18915581 is an equidigital number, since it uses as much as digits as its factorization.

18915581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 14400, while the sum is 38.

The square root of 18915581 is about 4349.2046399313. The cubic root of 18915581 is about 266.4443784716. Note that the first 3 decimals are identical.

The spelling of 18915581 in words is "eighteen million, nine hundred fifteen thousand, five hundred eighty-one".