21685733 has 2 divisors, whose sum is σ = 21685734. Its totient is φ = 21685732.

The previous prime is 21685721. The next prime is 21685739. The reversal of 21685733 is 33758612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19775809 + 1909924 = 4447^2 + 1382^2 .

It is a cyclic number.

It is not a de Polignac number, because 21685733 - 2¹⁶ = 21620197 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21685693 and 21685702.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21685739) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10842866 + 10842867.

It is an arithmetic number, because the mean of its divisors is an integer number (10842867).

Almost surely, 2^21685733 is an apocalyptic number.

It is an amenable number.

21685733 is a deficient number, since it is larger than the sum of its proper divisors (1).

21685733 is an equidigital number, since it uses as much as digits as its factorization.

21685733 is an evil number, because the sum of its binary digits is even.

The product of its digits is 30240, while the sum is 35.

The square root of 21685733 is about 4656.7942836247. The cubic root of 21685733 is about 278.8633040967.

The spelling of 21685733 in words is "twenty-one million, six hundred eighty-five thousand, seven hundred thirty-three".