78506821 has 2 divisors, whose sum is σ = 78506822. Its totient is φ = 78506820.

The previous prime is 78506819. The next prime is 78506839. The reversal of 78506821 is 12860587.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 61449921 + 17056900 = 7839^2 + 4130^2 .

It is a cyclic number.

It is not a de Polignac number, because 78506821 - 2¹ = 78506819 is a prime.

Together with 78506819, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78506801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39253410 + 39253411.

It is an arithmetic number, because the mean of its divisors is an integer number (39253411).

Almost surely, 2^78506821 is an apocalyptic number.

It is an amenable number.

78506821 is a deficient number, since it is larger than the sum of its proper divisors (1).

78506821 is an equidigital number, since it uses as much as digits as its factorization.

78506821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 26880, while the sum is 37.

The square root of 78506821 is about 8860.4074962724. The cubic root of 78506821 is about 428.1892868884.

The spelling of 78506821 in words is "seventy-eight million, five hundred six thousand, eight hundred twenty-one".