661812209 has 2 divisors, whose sum is σ = 661812210. Its totient is φ = 661812208.

The previous prime is 661812191. The next prime is 661812259. The reversal of 661812209 is 902218166.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 574800625 + 87011584 = 23975^2 + 9328^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-661812209 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (661812259) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330906104 + 330906105.

It is an arithmetic number, because the mean of its divisors is an integer number (330906105).

Almost surely, 2^661812209 is an apocalyptic number.

It is an amenable number.

661812209 is a deficient number, since it is larger than the sum of its proper divisors (1).

661812209 is an equidigital number, since it uses as much as digits as its factorization.

661812209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10368, while the sum is 35.

The square root of 661812209 is about 25725.7110494540. The cubic root of 661812209 is about 871.4549174756.

The spelling of 661812209 in words is "six hundred sixty-one million, eight hundred twelve thousand, two hundred nine".