18121921 has 2 divisors, whose sum is σ = 18121922. Its totient is φ = 18121920.

The previous prime is 18121891. The next prime is 18121973. The reversal of 18121921 is 12912181.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16524225 + 1597696 = 4065^2 + 1264^2 .

It is a cyclic number.

It is not a de Polignac number, because 18121921 - 2²¹ = 16024769 is a prime.

It is not a weakly prime, because it can be changed into another prime (18121721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9060960 + 9060961.

It is an arithmetic number, because the mean of its divisors is an integer number (9060961).

Almost surely, 2^18121921 is an apocalyptic number.

It is an amenable number.

18121921 is a deficient number, since it is larger than the sum of its proper divisors (1).

18121921 is an equidigital number, since it uses as much as digits as its factorization.

18121921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 288, while the sum is 25.

The square root of 18121921 is about 4256.9849659119. The cubic root of 18121921 is about 262.6645184862.

The spelling of 18121921 in words is "eighteen million, one hundred twenty-one thousand, nine hundred twenty-one".