861550821 has 12 divisors (see below), whose sum is σ = 1287375180. Its totient is φ = 554561280.

The previous prime is 861550787. The next prime is 861550831. The reversal of 861550821 is 128055168.

861550821 is a `hidden beast` number, since 86 + 1 + 550 + 8 + 21 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 304118721 + 557432100 = 17439^2 + 23610^2 .

It is not a de Polignac number, because 861550821 - 2⁶ = 861550757 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (861550831) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1650220 + ... + 1650741.

It is an arithmetic number, because the mean of its divisors is an integer number (107281265).

Almost surely, 2^861550821 is an apocalyptic number.

It is an amenable number.

861550821 is a deficient number, since it is larger than the sum of its proper divisors (425824359).

861550821 is a wasteful number, since it uses less digits than its factorization.

861550821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3300996 (or 3300993 counting only the distinct ones).

The product of its (nonzero) digits is 19200, while the sum is 36.

The square root of 861550821 is about 29352.1859662956. The cubic root of 861550821 is about 951.5398189762.

The spelling of 861550821 in words is "eight hundred sixty-one million, five hundred fifty thousand, eight hundred twenty-one".