11978415661 has 2 divisors, whose sum is σ = 11978415662. Its totient is φ = 11978415660.

The previous prime is 11978415649. The next prime is 11978415707. The reversal of 11978415661 is 16651487911.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 7213274761 + 4765140900 = 84931^2 + 69030^2 .

It is an emirp because it is prime and its reverse (16651487911) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 11978415661 - 2²³ = 11970027053 is a prime.

It is a super-3 number, since 3×11978415661³ (a number of 31 digits) contains 333 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (11978415601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5989207830 + 5989207831.

It is an arithmetic number, because the mean of its divisors is an integer number (5989207831).

Almost surely, 2^11978415661 is an apocalyptic number.

It is an amenable number.

11978415661 is a deficient number, since it is larger than the sum of its proper divisors (1).

11978415661 is an equidigital number, since it uses as much as digits as its factorization.

11978415661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 362880, while the sum is 49.

The spelling of 11978415661 in words is "eleven billion, nine hundred seventy-eight million, four hundred fifteen thousand, six hundred sixty-one".