78911981 has 2 divisors, whose sum is σ = 78911982. Its totient is φ = 78911980.

The previous prime is 78911953. The next prime is 78911993. The reversal of 78911981 is 18911987.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 41396356 + 37515625 = 6434^2 + 6125^2 .

It is an emirp because it is prime and its reverse (18911987) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-78911981 is a prime.

It is a super-2 number, since 2×78911981² = 12454201490688722, 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 (78911881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39455990 + 39455991.

It is an arithmetic number, because the mean of its divisors is an integer number (39455991).

Almost surely, 2^78911981 is an apocalyptic number.

It is an amenable number.

78911981 is a deficient number, since it is larger than the sum of its proper divisors (1).

78911981 is an equidigital number, since it uses as much as digits as its factorization.

78911981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 36288, while the sum is 44.

The square root of 78911981 is about 8883.2415817651. The cubic root of 78911981 is about 428.9246267386.

The spelling of 78911981 in words is "seventy-eight million, nine hundred eleven thousand, nine hundred eighty-one".