66261991 has 2 divisors, whose sum is σ = 66261992. Its totient is φ = 66261990.

The previous prime is 66261977. The next prime is 66262019. The reversal of 66261991 is 19916266.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 66261991 - 2¹¹ = 66259943 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66241991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33130995 + 33130996.

It is an arithmetic number, because the mean of its divisors is an integer number (33130996).

Almost surely, 2^66261991 is an apocalyptic number.

66261991 is a deficient number, since it is larger than the sum of its proper divisors (1).

66261991 is an equidigital number, since it uses as much as digits as its factorization.

66261991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 34992, while the sum is 40.

The square root of 66261991 is about 8140.1468659970. The cubic root of 66261991 is about 404.6580276415.

The spelling of 66261991 in words is "sixty-six million, two hundred sixty-one thousand, nine hundred ninety-one".