2178861 has 4 divisors (see below), whose sum is σ = 2905152. Its totient is φ = 1452572.

The previous prime is 2178829. The next prime is 2178877. The reversal of 2178861 is 1688712.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 2178861 - 2⁵ = 2178829 is a prime.

It is a D-number.

2178861 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2178461) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 363141 + ... + 363146.

It is an arithmetic number, because the mean of its divisors is an integer number (726288).

2^2178861 is an apocalyptic number.

It is an amenable number.

2178861 is a deficient number, since it is larger than the sum of its proper divisors (726291).

2178861 is an equidigital number, since it uses as much as digits as its factorization.

2178861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 726290.

The product of its digits is 5376, while the sum is 33.

The square root of 2178861 is about 1476.0965415582. The cubic root of 2178861 is about 129.6412396384.

Subtracting from 2178861 its sum of digits (33), we obtain a triangular number (2178828 = T₂₀₈₇).

The spelling of 2178861 in words is "two million, one hundred seventy-eight thousand, eight hundred sixty-one".