78221789 has 2 divisors, whose sum is σ = 78221790. Its totient is φ = 78221788.

The previous prime is 78221783. The next prime is 78221791. The reversal of 78221789 is 98712287.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 62141689 + 16080100 = 7883^2 + 4010^2 .

It is an emirp because it is prime and its reverse (98712287) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-78221789 is a prime.

It is a super-2 number, since 2×78221789² = 12237296548721042, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 78221791, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78221783) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39110894 + 39110895.

It is an arithmetic number, because the mean of its divisors is an integer number (39110895).

Almost surely, 2^78221789 is an apocalyptic number.

It is an amenable number.

78221789 is a deficient number, since it is larger than the sum of its proper divisors (1).

78221789 is an equidigital number, since it uses as much as digits as its factorization.

78221789 is an evil number, because the sum of its binary digits is even.

The product of its digits is 112896, while the sum is 44.

The square root of 78221789 is about 8844.3082827319. The cubic root of 78221789 is about 427.6704544667.

The spelling of 78221789 in words is "seventy-eight million, two hundred twenty-one thousand, seven hundred eighty-nine".