18031561 has 2 divisors, whose sum is σ = 18031562. Its totient is φ = 18031560.

The previous prime is 18031547. The next prime is 18031571. The reversal of 18031561 is 16513081.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12996025 + 5035536 = 3605^2 + 2244^2 .

It is a cyclic number.

It is not a de Polignac number, because 18031561 - 2¹⁵ = 17998793 is a prime.

It is a super-3 number, since 3×18031561³ (a number of 23 digits) contains 333 as substring.

It is not a weakly prime, because it can be changed into another prime (18031571) 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, 9015780 + 9015781.

It is an arithmetic number, because the mean of its divisors is an integer number (9015781).

Almost surely, 2^18031561 is an apocalyptic number.

It is an amenable number.

18031561 is a deficient number, since it is larger than the sum of its proper divisors (1).

18031561 is an equidigital number, since it uses as much as digits as its factorization.

18031561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 720, while the sum is 25.

The square root of 18031561 is about 4246.3585576350. The cubic root of 18031561 is about 262.2272226123.

It can be divided in two parts, 1803 and 1561, that added together give a square (3364 = 58²).

The spelling of 18031561 in words is "eighteen million, thirty-one thousand, five hundred sixty-one".