78021997 has 2 divisors, whose sum is σ = 78021998. Its totient is φ = 78021996.

The previous prime is 78021991. The next prime is 78022031. The reversal of 78021997 is 79912087.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 77951241 + 70756 = 8829^2 + 266^2 .

It is a cyclic number.

It is not a de Polignac number, because 78021997 - 2⁷ = 78021869 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78021991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39010998 + 39010999.

It is an arithmetic number, because the mean of its divisors is an integer number (39010999).

Almost surely, 2^78021997 is an apocalyptic number.

It is an amenable number.

78021997 is a deficient number, since it is larger than the sum of its proper divisors (1).

78021997 is an equidigital number, since it uses as much as digits as its factorization.

78021997 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 63504, while the sum is 43.

The square root of 78021997 is about 8833.0061134361. The cubic root of 78021997 is about 427.3060292122.

The spelling of 78021997 in words is "seventy-eight million, twenty-one thousand, nine hundred ninety-seven".