21817861 has 8 divisors (see below), whose sum is σ = 23555840. Its totient is φ = 20088432.

The previous prime is 21817853. The next prime is 21817867. The reversal of 21817861 is 16871812.

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

It is not a de Polignac number, because 21817861 - 2³ = 21817853 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 (21817867) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3796 + ... + 7618.

It is an arithmetic number, because the mean of its divisors is an integer number (2944480).

Almost surely, 2^21817861 is an apocalyptic number.

It is an amenable number.

21817861 is a deficient number, since it is larger than the sum of its proper divisors (1737979).

21817861 is a wasteful number, since it uses less digits than its factorization.

21817861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4275.

The product of its digits is 5376, while the sum is 34.

The square root of 21817861 is about 4670.9593233082. The cubic root of 21817861 is about 279.4285155070.

The spelling of 21817861 in words is "twenty-one million, eight hundred seventeen thousand, eight hundred sixty-one".