661949861 has 2 divisors, whose sum is σ = 661949862. Its totient is φ = 661949860.

The previous prime is 661949767. The next prime is 661949863. The reversal of 661949861 is 168949166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 537961636 + 123988225 = 23194^2 + 11135^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-661949861 is a prime.

Together with 661949863, 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 (661949863) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330974930 + 330974931.

It is an arithmetic number, because the mean of its divisors is an integer number (330974931).

Almost surely, 2^661949861 is an apocalyptic number.

It is an amenable number.

661949861 is a deficient number, since it is larger than the sum of its proper divisors (1).

661949861 is an equidigital number, since it uses as much as digits as its factorization.

661949861 is an evil number, because the sum of its binary digits is even.

The product of its digits is 559872, while the sum is 50.

The square root of 661949861 is about 25728.3862883003. The cubic root of 661949861 is about 871.5153319934.

The spelling of 661949861 in words is "six hundred sixty-one million, nine hundred forty-nine thousand, eight hundred sixty-one".