661427561 has 2 divisors, whose sum is σ = 661427562. Its totient is φ = 661427560.

The previous prime is 661427497. The next prime is 661427597. The reversal of 661427561 is 165724166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 607918336 + 53509225 = 24656^2 + 7315^2 .

It is a cyclic number.

It is not a de Polignac number, because 661427561 - 2⁶ = 661427497 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (661427861) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330713780 + 330713781.

It is an arithmetic number, because the mean of its divisors is an integer number (330713781).

Almost surely, 2^661427561 is an apocalyptic number.

It is an amenable number.

661427561 is a deficient number, since it is larger than the sum of its proper divisors (1).

661427561 is an equidigital number, since it uses as much as digits as its factorization.

661427561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 60480, while the sum is 38.

The square root of 661427561 is about 25718.2340179103. The cubic root of 661427561 is about 871.2860536861.

The spelling of 661427561 in words is "six hundred sixty-one million, four hundred twenty-seven thousand, five hundred sixty-one".