818878721 has 2 divisors, whose sum is σ = 818878722. Its totient is φ = 818878720.

The previous prime is 818878703. The next prime is 818878751. The reversal of 818878721 is 127878818.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 435306496 + 383572225 = 20864^2 + 19585^2 .

It is a cyclic number.

It is not a de Polignac number, because 818878721 - 2⁶ = 818878657 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 818878721.

It is not a weakly prime, because it can be changed into another prime (818878751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 409439360 + 409439361.

It is an arithmetic number, because the mean of its divisors is an integer number (409439361).

Almost surely, 2^818878721 is an apocalyptic number.

It is an amenable number.

818878721 is a deficient number, since it is larger than the sum of its proper divisors (1).

818878721 is an equidigital number, since it uses as much as digits as its factorization.

818878721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 401408, while the sum is 50.

The square root of 818878721 is about 28616.0570484475. The cubic root of 818878721 is about 935.5633392058.

The spelling of 818878721 in words is "eight hundred eighteen million, eight hundred seventy-eight thousand, seven hundred twenty-one".