18218621 has 4 divisors (see below), whose sum is σ = 18313212. Its totient is φ = 18124032.

The previous prime is 18218617. The next prime is 18218639. The reversal of 18218621 is 12681281.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12681281 = 919 ⋅13799.

It can be written as a sum of positive squares in 2 ways, for example, as 5359225 + 12859396 = 2315^2 + 3586^2 .

It is a cyclic number.

It is not a de Polignac number, because 18218621 - 2² = 18218617 is a prime.

It is a super-2 number, since 2×18218621² = 663836302283282, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18218821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 47006 + ... + 47391.

It is an arithmetic number, because the mean of its divisors is an integer number (4578303).

Almost surely, 2^18218621 is an apocalyptic number.

It is an amenable number.

18218621 is a deficient number, since it is larger than the sum of its proper divisors (94591).

18218621 is an equidigital number, since it uses as much as digits as its factorization.

18218621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 94590.

The product of its digits is 1536, while the sum is 29.

The square root of 18218621 is about 4268.3276584630. The cubic root of 18218621 is about 263.1308894667.

The spelling of 18218621 in words is "eighteen million, two hundred eighteen thousand, six hundred twenty-one".