661465781 has 2 divisors, whose sum is σ = 661465782. Its totient is φ = 661465780.

The previous prime is 661465771. The next prime is 661465789. The reversal of 661465781 is 187564166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 586366225 + 75099556 = 24215^2 + 8666^2 .

It is a cyclic number.

It is not a de Polignac number, because 661465781 - 2¹⁰ = 661464757 is a prime.

It is a super-2 number, since 2×661465781² = 875073958867879922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661465789) 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, 330732890 + 330732891.

It is an arithmetic number, because the mean of its divisors is an integer number (330732891).

Almost surely, 2^661465781 is an apocalyptic number.

It is an amenable number.

661465781 is a deficient number, since it is larger than the sum of its proper divisors (1).

661465781 is an equidigital number, since it uses as much as digits as its factorization.

661465781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 241920, while the sum is 44.

The square root of 661465781 is about 25718.9770597510. The cubic root of 661465781 is about 871.3028355246.

The spelling of 661465781 in words is "six hundred sixty-one million, four hundred sixty-five thousand, seven hundred eighty-one".