18931221 has 12 divisors (see below), whose sum is σ = 27675648. Its totient is φ = 12468264.

The previous prime is 18931207. The next prime is 18931243. The reversal of 18931221 is 12213981.

It is not a de Polignac number, because 18931221 - 2¹¹ = 18929173 is a prime.

It is a super-2 number, since 2×18931221² = 716782257101682, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18931261) 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 11 ways as a sum of consecutive naturals, for example, 11925 + ... + 13418.

It is an arithmetic number, because the mean of its divisors is an integer number (2306304).

Almost surely, 2^18931221 is an apocalyptic number.

It is an amenable number.

18931221 is a deficient number, since it is larger than the sum of its proper divisors (8744427).

18931221 is a wasteful number, since it uses less digits than its factorization.

18931221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25432 (or 25429 counting only the distinct ones).

The product of its digits is 864, while the sum is 27.

The square root of 18931221 is about 4351.0022983216. The cubic root of 18931221 is about 266.5177931182.

The spelling of 18931221 in words is "eighteen million, nine hundred thirty-one thousand, two hundred twenty-one".