@Daedalus sir,
Thank you sir for helping.
But there is a mistake in the f(x) which you have solved. It gives the nearly correct value for f(1)=2.9.... , f(2)=2.9...., but from f(3) to f(12) it gives the value so absurd.
Could it be expressed in trigonometric function? Actually I expect it in a more simplified form.
If we plot the points (1,3), (2,3), (3,6), (4,1), (5,4), (6,6), (7,2), (8,5), (9,0), (10,3), (11,5), (12,1) on graph paper, we get a sin or cos like curve (nearly). Plz help.