21686947 has 2 divisors, whose sum is σ = 21686948. Its totient is φ = 21686946.

The previous prime is 21686939. The next prime is 21686957. The reversal of 21686947 is 74968612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21686947 - 2³ = 21686939 is a prime.

It is not a weakly prime, because it can be changed into another prime (21686927) 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 as a sum of consecutive naturals, namely, 10843473 + 10843474.

It is an arithmetic number, because the mean of its divisors is an integer number (10843474).

Almost surely, 2^21686947 is an apocalyptic number.

21686947 is a deficient number, since it is larger than the sum of its proper divisors (1).

21686947 is an equidigital number, since it uses as much as digits as its factorization.

21686947 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 145152, while the sum is 43.

The square root of 21686947 is about 4656.9246289799. The cubic root of 21686947 is about 278.8685077288.

The spelling of 21686947 in words is "twenty-one million, six hundred eighty-six thousand, nine hundred forty-seven".