661115881 has 2 divisors, whose sum is σ = 661115882. Its totient is φ = 661115880.

The previous prime is 661115869. The next prime is 661115891. The reversal of 661115881 is 188511166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 595360000 + 65755881 = 24400^2 + 8109^2 .

It is a cyclic number.

It is not a de Polignac number, because 661115881 - 2⁷ = 661115753 is a prime.

It is a super-2 number, since 2×661115881² = 874148416220812322, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 661115881.

It is not a weakly prime, because it can be changed into another prime (661115891) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330557940 + 330557941.

It is an arithmetic number, because the mean of its divisors is an integer number (330557941).

Almost surely, 2^661115881 is an apocalyptic number.

It is an amenable number.

661115881 is a deficient number, since it is larger than the sum of its proper divisors (1).

661115881 is an equidigital number, since it uses as much as digits as its factorization.

661115881 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 11520, while the sum is 37.

The square root of 661115881 is about 25712.1737898607. The cubic root of 661115881 is about 871.1491754549.

The spelling of 661115881 in words is "six hundred sixty-one million, one hundred fifteen thousand, eight hundred eighty-one".