865123821 has 40 divisors (see below), whose sum is σ = 1329512184. Its totient is φ = 560286720.

The previous prime is 865123807. The next prime is 865123841. The reversal of 865123821 is 128321568.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 63441225 + 801682596 = 7965^2 + 28314^2 .

It is not a de Polignac number, because 865123821 - 2¹⁸ = 864861677 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (865123801) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 1118791 + ... + 1119563.

Almost surely, 2^865123821 is an apocalyptic number.

865123821 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

It is an amenable number.

865123821 is a deficient number, since it is larger than the sum of its proper divisors (464388363).

865123821 is a wasteful number, since it uses less digits than its factorization.

865123821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1163 (or 1154 counting only the distinct ones).

The product of its digits is 23040, while the sum is 36.

The square root of 865123821 is about 29412.9872845313. The cubic root of 865123821 is about 952.8534047276.

The spelling of 865123821 in words is "eight hundred sixty-five million, one hundred twenty-three thousand, eight hundred twenty-one".