21686449 has 2 divisors, whose sum is σ = 21686450. Its totient is φ = 21686448.

The previous prime is 21686443. The next prime is 21686471. The reversal of 21686449 is 94468612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21669025 + 17424 = 4655^2 + 132^2 .

It is a cyclic number.

It is not a de Polignac number, because 21686449 - 2¹³ = 21678257 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21686443) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10843224 + 10843225.

It is an arithmetic number, because the mean of its divisors is an integer number (10843225).

Almost surely, 2^21686449 is an apocalyptic number.

It is an amenable number.

21686449 is a deficient number, since it is larger than the sum of its proper divisors (1).

21686449 is an equidigital number, since it uses as much as digits as its factorization.

21686449 is an evil number, because the sum of its binary digits is even.

The product of its digits is 82944, while the sum is 40.

The square root of 21686449 is about 4656.8711599098. The cubic root of 21686449 is about 278.8663731487.

The spelling of 21686449 in words is "twenty-one million, six hundred eighty-six thousand, four hundred forty-nine".