66311561 has 2 divisors, whose sum is σ = 66311562. Its totient is φ = 66311560.

The previous prime is 66311551. The next prime is 66311569. The reversal of 66311561 is 16511366.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 66015625 + 295936 = 8125^2 + 544^2 .

It is a cyclic number.

It is not a de Polignac number, because 66311561 - 2¹⁰ = 66310537 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (66311569) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33155780 + 33155781.

It is an arithmetic number, because the mean of its divisors is an integer number (33155781).

Almost surely, 2^66311561 is an apocalyptic number.

It is an amenable number.

66311561 is a deficient number, since it is larger than the sum of its proper divisors (1).

66311561 is an equidigital number, since it uses as much as digits as its factorization.

66311561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3240, while the sum is 29.

The square root of 66311561 is about 8143.1910821250. The cubic root of 66311561 is about 404.7589095008.

It can be divided in two parts, 6631 and 1561, that added together give a 13-th power (8192 = 2¹³).

The spelling of 66311561 in words is "sixty-six million, three hundred eleven thousand, five hundred sixty-one".