78921989 has 2 divisors, whose sum is σ = 78921990. Its totient is φ = 78921988.

The previous prime is 78921971. The next prime is 78922031. The reversal of 78921989 is 98912987.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 69588964 + 9333025 = 8342^2 + 3055^2 .

It is a cyclic number.

It is not a de Polignac number, because 78921989 - 2²⁴ = 62144773 is a prime.

It is a super-2 number, since 2×78921989² = 12457360695432242, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 78921989.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78921949) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39460994 + 39460995.

It is an arithmetic number, because the mean of its divisors is an integer number (39460995).

Almost surely, 2^78921989 is an apocalyptic number.

It is an amenable number.

78921989 is a deficient number, since it is larger than the sum of its proper divisors (1).

78921989 is an equidigital number, since it uses as much as digits as its factorization.

78921989 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 653184, while the sum is 53.

The square root of 78921989 is about 8883.8048717878. The cubic root of 78921989 is about 428.9427587390.

The spelling of 78921989 in words is "seventy-eight million, nine hundred twenty-one thousand, nine hundred eighty-nine".