66421721 has 2 divisors, whose sum is σ = 66421722. Its totient is φ = 66421720.

The previous prime is 66421717. The next prime is 66421753. The reversal of 66421721 is 12712466.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 64561225 + 1860496 = 8035^2 + 1364^2 .

It is a cyclic number.

It is not a de Polignac number, because 66421721 - 2² = 66421717 is a prime.

It is not a weakly prime, because it can be changed into another prime (66420721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33210860 + 33210861.

It is an arithmetic number, because the mean of its divisors is an integer number (33210861).

Almost surely, 2^66421721 is an apocalyptic number.

It is an amenable number.

66421721 is a deficient number, since it is larger than the sum of its proper divisors (1).

66421721 is an equidigital number, since it uses as much as digits as its factorization.

66421721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4032, while the sum is 29.

The square root of 66421721 is about 8149.9522084488. The cubic root of 66421721 is about 404.9829205824.

The spelling of 66421721 in words is "sixty-six million, four hundred twenty-one thousand, seven hundred twenty-one".