861821 has 8 divisors (see below), whose sum is σ = 922080. Its totient is φ = 803088.

The previous prime is 861803. The next prime is 861823. The reversal of 861821 is 128168.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-861821 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (861823) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 935 + ... + 1611.

It is an arithmetic number, because the mean of its divisors is an integer number (115260).

2⁸⁶¹⁸²¹ is an apocalyptic number.

It is an amenable number.

861821 is a deficient number, since it is larger than the sum of its proper divisors (60259).

861821 is a wasteful number, since it uses less digits than its factorization.

861821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 763.

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

The square root of 861821 is about 928.3431477638. The cubic root of 861821 is about 95.1639274981.

Adding to 861821 its reverse (128168), we get a palindrome (989989).

The spelling of 861821 in words is "eight hundred sixty-one thousand, eight hundred twenty-one".