66199981 has 2 divisors, whose sum is σ = 66199982. Its totient is φ = 66199980.

The previous prime is 66199979. The next prime is 66199997. The reversal of 66199981 is 18999166.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 66161956 + 38025 = 8134^2 + 195^2 .

It is a cyclic number.

It is not a de Polignac number, because 66199981 - 2¹ = 66199979 is a prime.

It is a super-2 number, since 2×66199981² = 8764874968800722, which contains 22 as substring.

Together with 66199979, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66199961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33099990 + 33099991.

It is an arithmetic number, because the mean of its divisors is an integer number (33099991).

Almost surely, 2^66199981 is an apocalyptic number.

It is an amenable number.

66199981 is a deficient number, since it is larger than the sum of its proper divisors (1).

66199981 is an equidigital number, since it uses as much as digits as its factorization.

66199981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 209952, while the sum is 49.

The square root of 66199981 is about 8136.3370751217. The cubic root of 66199981 is about 404.5317577869.

The spelling of 66199981 in words is "sixty-six million, one hundred ninety-nine thousand, nine hundred eighty-one".