78389921 has 2 divisors, whose sum is σ = 78389922. Its totient is φ = 78389920.

The previous prime is 78389891. The next prime is 78389947. The reversal of 78389921 is 12998387.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 52998400 + 25391521 = 7280^2 + 5039^2 .

It is a cyclic number.

It is not a de Polignac number, because 78389921 - 2¹⁰ = 78388897 is a prime.

It is a super-2 number, since 2×78389921² = 12289959428772482, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (78389951) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39194960 + 39194961.

It is an arithmetic number, because the mean of its divisors is an integer number (39194961).

Almost surely, 2^78389921 is an apocalyptic number.

It is an amenable number.

78389921 is a deficient number, since it is larger than the sum of its proper divisors (1).

78389921 is an equidigital number, since it uses as much as digits as its factorization.

78389921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 217728, while the sum is 47.

The square root of 78389921 is about 8853.8082766683. The cubic root of 78389921 is about 427.9766506172.

The spelling of 78389921 in words is "seventy-eight million, three hundred eighty-nine thousand, nine hundred twenty-one".