66691621 has 2 divisors, whose sum is σ = 66691622. Its totient is φ = 66691620.

The previous prime is 66691609. The next prime is 66691643. The reversal of 66691621 is 12619666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 62631396 + 4060225 = 7914^2 + 2015^2 .

It is a cyclic number.

It is not a de Polignac number, because 66691621 - 2⁹ = 66691109 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66691321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33345810 + 33345811.

It is an arithmetic number, because the mean of its divisors is an integer number (33345811).

Almost surely, 2^66691621 is an apocalyptic number.

It is an amenable number.

66691621 is a deficient number, since it is larger than the sum of its proper divisors (1).

66691621 is an equidigital number, since it uses as much as digits as its factorization.

66691621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 23328, while the sum is 37.

The square root of 66691621 is about 8166.4938008915. The cubic root of 66691621 is about 405.5307191590.

The spelling of 66691621 in words is "sixty-six million, six hundred ninety-one thousand, six hundred twenty-one".