78644140021 has 2 divisors, whose sum is σ = 78644140022. Its totient is φ = 78644140020.

The previous prime is 78644140009. The next prime is 78644140067. The reversal of 78644140021 is 12004144687.

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., 52654186225 + 25989953796 = 229465^2 + 161214^2 .

It is a cyclic number.

It is not a de Polignac number, because 78644140021 - 2²³ = 78635751413 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78644140321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39322070010 + 39322070011.

It is an arithmetic number, because the mean of its divisors is an integer number (39322070011).

Almost surely, 2^78644140021 is an apocalyptic number.

It is an amenable number.

78644140021 is a deficient number, since it is larger than the sum of its proper divisors (1).

78644140021 is an equidigital number, since it uses as much as digits as its factorization.

78644140021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 43008, while the sum is 37.

The spelling of 78644140021 in words is "seventy-eight billion, six hundred forty-four million, one hundred forty thousand, twenty-one".