18151561 has 4 divisors (see below), whose sum is σ = 18594324. Its totient is φ = 17708800.

The previous prime is 18151537. The next prime is 18151579. The reversal of 18151561 is 16515181.

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 553536 + 17598025 = 744^2 + 4195^2 .

It is a cyclic number.

It is not a de Polignac number, because 18151561 - 2⁷ = 18151433 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18151501) 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 in 3 ways as a sum of consecutive naturals, for example, 221320 + ... + 221401.

It is an arithmetic number, because the mean of its divisors is an integer number (4648581).

Almost surely, 2^18151561 is an apocalyptic number.

It is an amenable number.

18151561 is a deficient number, since it is larger than the sum of its proper divisors (442763).

18151561 is an equidigital number, since it uses as much as digits as its factorization.

18151561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 442762.

The product of its digits is 1200, while the sum is 28.

The square root of 18151561 is about 4260.4648807378. The cubic root of 18151561 is about 262.8076441446.

The spelling of 18151561 in words is "eighteen million, one hundred fifty-one thousand, five hundred sixty-one".