18735721421 has 2 divisors, whose sum is σ = 18735721422. Its totient is φ = 18735721420.

The previous prime is 18735721397. The next prime is 18735721427. The reversal of 18735721421 is 12412753781.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15160996900 + 3574724521 = 123130^2 + 59789^2 .

It is a cyclic number.

It is not a de Polignac number, because 18735721421 - 2²² = 18731527117 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18735721427) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9367860710 + 9367860711.

It is an arithmetic number, because the mean of its divisors is an integer number (9367860711).

Almost surely, 2^18735721421 is an apocalyptic number.

It is an amenable number.

18735721421 is a deficient number, since it is larger than the sum of its proper divisors (1).

18735721421 is an equidigital number, since it uses as much as digits as its factorization.

18735721421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 94080, while the sum is 41.

The spelling of 18735721421 in words is "eighteen billion, seven hundred thirty-five million, seven hundred twenty-one thousand, four hundred twenty-one".