821861 has 2 divisors, whose sum is σ = 821862. Its totient is φ = 821860.

The previous prime is 821857. The next prime is 821869. The reversal of 821861 is 168128.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 649636 + 172225 = 806^2 + 415^2 .

It is a cyclic number.

It is not a de Polignac number, because 821861 - 2² = 821857 is a prime.

It is a plaindrome in base 15.

It is a self number, because there is not a number n which added to its sum of digits gives 821861.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (821869) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 410930 + 410931.

It is an arithmetic number, because the mean of its divisors is an integer number (410931).

2⁸²¹⁸⁶¹ is an apocalyptic number.

It is an amenable number.

821861 is a deficient number, since it is larger than the sum of its proper divisors (1).

821861 is an equidigital number, since it uses as much as digits as its factorization.

821861 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 768, while the sum is 26.

The square root of 821861 is about 906.5654968065. The cubic root of 821861 is about 93.6697707685.

Adding to 821861 its reverse (168128), we get a palindrome (989989).

The spelling of 821861 in words is "eight hundred twenty-one thousand, eight hundred sixty-one".