21187261 has 8 divisors (see below), whose sum is σ = 22821920. Its totient is φ = 19604592.

The previous prime is 21187259. The next prime is 21187279. The reversal of 21187261 is 16278112.

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 21187261 - 2¹ = 21187259 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 (21187211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12150 + ... + 13783.

It is an arithmetic number, because the mean of its divisors is an integer number (2852740).

Almost surely, 2^21187261 is an apocalyptic number.

It is an amenable number.

21187261 is a deficient number, since it is larger than the sum of its proper divisors (1634659).

21187261 is a wasteful number, since it uses less digits than its factorization.

21187261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25995.

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

The square root of 21187261 is about 4602.9621984109. The cubic root of 21187261 is about 276.7100538398.

The spelling of 21187261 in words is "twenty-one million, one hundred eighty-seven thousand, two hundred sixty-one".