16661326421 has 2 divisors, whose sum is σ = 16661326422. Its totient is φ = 16661326420.

The previous prime is 16661326411. The next prime is 16661326447. The reversal of 16661326421 is 12462316661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16252680196 + 408646225 = 127486^2 + 20215^2 .

It is an emirp because it is prime and its reverse (12462316661) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-16661326421 is a prime.

It is a super-2 number, since 2×16661326421² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16661326411) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8330663210 + 8330663211.

It is an arithmetic number, because the mean of its divisors is an integer number (8330663211).

Almost surely, 2^16661326421 is an apocalyptic number.

It is an amenable number.

16661326421 is a deficient number, since it is larger than the sum of its proper divisors (1).

16661326421 is an equidigital number, since it uses as much as digits as its factorization.

16661326421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 62208, while the sum is 38.

The spelling of 16661326421 in words is "sixteen billion, six hundred sixty-one million, three hundred twenty-six thousand, four hundred twenty-one".