18211861 has 4 divisors (see below), whose sum is σ = 19170400. Its totient is φ = 17253324.

The previous prime is 18211859. The next prime is 18211877. The reversal of 18211861 is 16811281.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 18211861 - 2¹ = 18211859 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18212861) 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, 479241 + ... + 479278.

It is an arithmetic number, because the mean of its divisors is an integer number (4792600).

Almost surely, 2^18211861 is an apocalyptic number.

18211861 is the 1909-th centered decagonal number.

It is an amenable number.

18211861 is a deficient number, since it is larger than the sum of its proper divisors (958539).

18211861 is an equidigital number, since it uses as much as digits as its factorization.

18211861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 958538.

The product of its digits is 768, while the sum is 28.

The square root of 18211861 is about 4267.5357057674. The cubic root of 18211861 is about 263.0983406281.

The spelling of 18211861 in words is "eighteen million, two hundred eleven thousand, eight hundred sixty-one".