78637921 has 2 divisors, whose sum is σ = 78637922. Its totient is φ = 78637920.

The previous prime is 78637907. The next prime is 78637963. The reversal of 78637921 is 12973687.

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., 59845696 + 18792225 = 7736^2 + 4335^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-78637921 is a prime.

It is not a weakly prime, because it can be changed into another prime (78637901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39318960 + 39318961.

It is an arithmetic number, because the mean of its divisors is an integer number (39318961).

Almost surely, 2^78637921 is an apocalyptic number.

It is an amenable number.

78637921 is a deficient number, since it is larger than the sum of its proper divisors (1).

78637921 is an equidigital number, since it uses as much as digits as its factorization.

78637921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 127008, while the sum is 43.

The square root of 78637921 is about 8867.8024899070. The cubic root of 78637921 is about 428.4275014217.

The spelling of 78637921 in words is "seventy-eight million, six hundred thirty-seven thousand, nine hundred twenty-one".