S = n = 0 ∑ ∞ [ ( n 2 n ) 2 2 5 n H n ]
S can be represented as
B Γ 2 ( D C ) π A ( E π − F lo g G )
where A , B , C , D , E , F and G are positive integers, g cd ( C , D ) = g cd ( B , E ) = 1 and G is a prime number.
Evaluate A + B + C + D + E + F + G
See Also : Part 1
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The complete elliptic function of the first kind (under one convention) is K ( k ) = ∫ 0 2 1 π 1 − k 2 sin 2 θ d θ = 2 1 π n = 0 ∑ ∞ ( n 2 n ) 2 2 4 n k 2 n so that n = 0 ∑ ∞ ( n 2 n ) 2 2 5 n k n = π 2 K ( 2 k ) Thus, if we write S = n = 1 ∑ ∞ ( n 2 n ) 2 2 5 n H n then S = = = = = n = 1 ∑ ∞ ( n 2 n ) 2 2 − 5 n ∫ 0 1 1 − k 1 − k n d k = π 2 ∫ 0 1 1 − k K ( 2 1 ) − K ( 2 k ) d k π 2 ∫ 0 1 1 − k d k ∫ 0 2 1 π ⎩ ⎨ ⎧ 1 − 2 1 sin 2 θ 1 − 1 − 2 1 k sin 2 θ 1 ⎭ ⎬ ⎫ d θ π 1 ∫ 0 1 d k ∫ 0 2 1 π ( 1 − 2 1 sin 2 θ ) ( 1 − 2 1 k sin 2 θ ) ( 1 − 2 1 sin 2 θ + 1 − 2 1 k sin 2 θ ) sin 2 θ d θ π 1 ∫ 0 2 1 π 1 − 2 1 sin 2 θ sin 2 θ d θ ⎝ ⎜ ⎛ ∫ 0 1 1 − 2 1 k sin 2 θ ( 1 − 2 1 sin 2 θ + 1 − 2 1 k sin 2 θ ) d k ⎠ ⎟ ⎞ π 2 ∫ 0 2 1 π 1 − 2 1 sin 2 θ d θ { 2 ln ( 1 + 1 − 2 1 sin 2 θ ) − 2 ln 2 − ln ( 1 − 2 1 sin 2 θ ) } Since 2 1 is equal to its own complement, we have (Gradshteyn and Rhyzik) ∫ 0 2 1 π 1 − 2 1 sin 2 θ ln ( 1 + 1 − 2 1 sin 2 θ ) d θ = 4 1 ( π − ln 2 ) K ( 2 1 ) while this paper tells us that ∫ 0 2 1 π 1 − 2 1 sin 2 θ ln ( 1 − 2 1 sin 2 θ ) d θ = − 2 1 ln 2 K ( 2 1 ) (on further looking, this integral is in G&R as well) and hence S = = π 2 [ 2 × 4 1 ( π − ln 2 ) K ( 2 1 ) − 2 ln 2 K ( 2 1 ) + 2 1 ln 2 K ( 2 1 ) ] π 1 K ( 2 1 ) ( π − 4 ln 2 ) = 2 Γ ( 4 3 ) 2 π ( π − 4 ln 2 ) making the answer 1 + 2 + 3 + 4 + 1 + 4 + 2 = 1 7 .