18661681 has 2 divisors, whose sum is σ = 18661682. Its totient is φ = 18661680.

The previous prime is 18661673. The next prime is 18661693. The reversal of 18661681 is 18616681.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 9511056 + 9150625 = 3084^2 + 3025^2 .

It is an emirp because it is prime and its reverse (18616681) is a distict prime. It is also a bemirp because it and its reverse can be mirrored producing other two distinct primes, 18919981 and 18991981.

It is a cyclic number.

It is not a de Polignac number, because 18661681 - 2³ = 18661673 is a prime.

It is a super-2 number, since 2×18661681² = 696516675491522, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 18661681.

It is not a weakly prime, because it can be changed into another prime (18661661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9330840 + 9330841.

It is an arithmetic number, because the mean of its divisors is an integer number (9330841).

Almost surely, 2^18661681 is an apocalyptic number.

It is an amenable number.

18661681 is a deficient number, since it is larger than the sum of its proper divisors (1).

18661681 is an equidigital number, since it uses as much as digits as its factorization.

18661681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 13824, while the sum is 37.

The square root of 18661681 is about 4319.9167816059. The cubic root of 18661681 is about 265.2468614558.

The spelling of 18661681 in words is "eighteen million, six hundred sixty-one thousand, six hundred eighty-one".