21178261 has 8 divisors (see below), whose sum is σ = 22843800. Its totient is φ = 19517952.

The previous prime is 21178229. The next prime is 21178273. The reversal of 21178261 is 16287112.

It can be written as a sum of positive squares in 4 ways, for example, as 874225 + 20304036 = 935^2 + 4506^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21178261 - 2⁵ = 21178229 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 (21178211) 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, 12861 + ... + 14413.

It is an arithmetic number, because the mean of its divisors is an integer number (2855475).

Almost surely, 2^21178261 is an apocalyptic number.

It is an amenable number.

21178261 is a deficient number, since it is larger than the sum of its proper divisors (1665539).

21178261 is a wasteful number, since it uses less digits than its factorization.

21178261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2615.

The product of its digits is 1344, while the sum is 28.

The square root of 21178261 is about 4601.9844632506. The cubic root of 21178261 is about 276.6708676642.

The spelling of 21178261 in words is "twenty-one million, one hundred seventy-eight thousand, two hundred sixty-one".