21686249 has 6 divisors (see below), whose sum is σ = 23482926. Its totient is φ = 20017920.

The previous prime is 21686243. The next prime is 21686257. The reversal of 21686249 is 94268612.

It can be written as a sum of positive squares in 3 ways, for example, as 110224 + 21576025 = 332^2 + 4645^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21686249 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21686243) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 63992 + ... + 64329.

It is an arithmetic number, because the mean of its divisors is an integer number (3913821).

Almost surely, 2^21686249 is an apocalyptic number.

It is an amenable number.

21686249 is a deficient number, since it is larger than the sum of its proper divisors (1796677).

21686249 is a wasteful number, since it uses less digits than its factorization.

21686249 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128347 (or 128334 counting only the distinct ones).

The product of its digits is 41472, while the sum is 38.

The square root of 21686249 is about 4656.8496862149. The cubic root of 21686249 is about 278.8655158784.

The spelling of 21686249 in words is "twenty-one million, six hundred eighty-six thousand, two hundred forty-nine".