78671821 has 2 divisors, whose sum is σ = 78671822. Its totient is φ = 78671820.

The previous prime is 78671797. The next prime is 78671861. The reversal of 78671821 is 12817687.

It is an a-pointer prime, because the next prime (78671861) can be obtained adding 78671821 to its sum of digits (40).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 58690921 + 19980900 = 7661^2 + 4470^2 .

It is an emirp because it is prime and its reverse (12817687) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 78671821 - 2¹⁹ = 78147533 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78671861) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39335910 + 39335911.

It is an arithmetic number, because the mean of its divisors is an integer number (39335911).

Almost surely, 2^78671821 is an apocalyptic number.

It is an amenable number.

78671821 is a deficient number, since it is larger than the sum of its proper divisors (1).

78671821 is an equidigital number, since it uses as much as digits as its factorization.

78671821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 37632, while the sum is 40.

The square root of 78671821 is about 8869.7136932372. The cubic root of 78671821 is about 428.4890561424.

The spelling of 78671821 in words is "seventy-eight million, six hundred seventy-one thousand, eight hundred twenty-one".