66655991 has 2 divisors, whose sum is σ = 66655992. Its totient is φ = 66655990.

The previous prime is 66655969. The next prime is 66655999. The reversal of 66655991 is 19955666.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66655991 is a prime.

It is a super-2 number, since 2×66655991² = 8886042272384162, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66655999) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33327995 + 33327996.

It is an arithmetic number, because the mean of its divisors is an integer number (33327996).

Almost surely, 2^66655991 is an apocalyptic number.

66655991 is a deficient number, since it is larger than the sum of its proper divisors (1).

66655991 is an equidigital number, since it uses as much as digits as its factorization.

66655991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 437400, while the sum is 47.

The square root of 66655991 is about 8164.3120347032. The cubic root of 66655991 is about 405.4584880291.

The spelling of 66655991 in words is "sixty-six million, six hundred fifty-five thousand, nine hundred ninety-one".