11661187781 has 2 divisors, whose sum is σ = 11661187782. Its totient is φ = 11661187780.

The previous prime is 11661187777. The next prime is 11661187847. The reversal of 11661187781 is 18778116611.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 7264834756 + 4396353025 = 85234^2 + 66305^2 .

It is a cyclic number.

It is not a de Polignac number, because 11661187781 - 2² = 11661187777 is a prime.

It is a super-2 number, since 2×11661187781² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (11661180781) 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, 5830593890 + 5830593891.

It is an arithmetic number, because the mean of its divisors is an integer number (5830593891).

Almost surely, 2^11661187781 is an apocalyptic number.

It is an amenable number.

11661187781 is a deficient number, since it is larger than the sum of its proper divisors (1).

11661187781 is an equidigital number, since it uses as much as digits as its factorization.

11661187781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 112896, while the sum is 47.

The spelling of 11661187781 in words is "eleven billion, six hundred sixty-one million, one hundred eighty-seven thousand, seven hundred eighty-one".