861687821 has 2 divisors, whose sum is σ = 861687822. Its totient is φ = 861687820.

The previous prime is 861687797. The next prime is 861687877. The reversal of 861687821 is 128786168.

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., 440412196 + 421275625 = 20986^2 + 20525^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-861687821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (861687521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 430843910 + 430843911.

It is an arithmetic number, because the mean of its divisors is an integer number (430843911).

Almost surely, 2^861687821 is an apocalyptic number.

It is an amenable number.

861687821 is a deficient number, since it is larger than the sum of its proper divisors (1).

861687821 is an equidigital number, since it uses as much as digits as its factorization.

861687821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 258048, while the sum is 47.

The square root of 861687821 is about 29354.5196009064. The cubic root of 861687821 is about 951.5902528538.

The spelling of 861687821 in words is "eight hundred sixty-one million, six hundred eighty-seven thousand, eight hundred twenty-one".