66691643 has 2 divisors, whose sum is σ = 66691644. Its totient is φ = 66691642.

The previous prime is 66691621. The next prime is 66691657. The reversal of 66691643 is 34619666.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 66691643 - 2¹⁸ = 66429499 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 66691643.

It is not a weakly prime, because it can be changed into another prime (66691693) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33345821 + 33345822.

It is an arithmetic number, because the mean of its divisors is an integer number (33345822).

Almost surely, 2^66691643 is an apocalyptic number.

66691643 is a deficient number, since it is larger than the sum of its proper divisors (1).

66691643 is an equidigital number, since it uses as much as digits as its factorization.

66691643 is an evil number, because the sum of its binary digits is even.

The product of its digits is 139968, while the sum is 41.

The square root of 66691643 is about 8166.4951478587. The cubic root of 66691643 is about 405.5307637507.

The spelling of 66691643 in words is "sixty-six million, six hundred ninety-one thousand, six hundred forty-three".