66691321 has 2 divisors, whose sum is σ = 66691322. Its totient is φ = 66691320.

The previous prime is 66691309. The next prime is 66691333. The reversal of 66691321 is 12319666.

It is a balanced prime because it is at equal distance from previous prime (66691309) and next prime (66691333).

It can be written as a sum of positive squares in only one way, i.e., 55056400 + 11634921 = 7420^2 + 3411^2 .

It is a cyclic number.

It is not a de Polignac number, because 66691321 - 2²⁵ = 33136889 is a prime.

It is not a weakly prime, because it can be changed into another prime (66691301) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33345660 + 33345661.

It is an arithmetic number, because the mean of its divisors is an integer number (33345661).

Almost surely, 2^66691321 is an apocalyptic number.

It is an amenable number.

66691321 is a deficient number, since it is larger than the sum of its proper divisors (1).

66691321 is an equidigital number, since it uses as much as digits as its factorization.

66691321 is an evil number, because the sum of its binary digits is even.

The product of its digits is 11664, while the sum is 34.

The square root of 66691321 is about 8166.4754331352. The cubic root of 66691321 is about 405.5301110897.

The spelling of 66691321 in words is "sixty-six million, six hundred ninety-one thousand, three hundred twenty-one".