Euler #44

	#load "euler.cma";;
	open Euler;;
	let pentagonal n = n * (3*n - 1) / 2;;
	let pentagonal_index n = int_of_float ((1. +. sqrt(1. +. 24. *. float_of_int(n))) /. 6.);;
	let is_pentagonal d = (mod_float ((sqrt(24. *. float_of_int(d) +. 1.) +. 1.) /. 6.) 1.) = 0.;;
	let get_pentagonals n = List.rev_map (pentagonal) (range n);;
	let low_pentagonals n =
	let idx = pentagonal_index n in
	get_pentagonals (idx-1);;
	let rec search_pentagonal l = match l with
	[] -> raise Not_found
	| h :: t ->
	let low = low_pentagonals h in
	let sums = List.filter (fun x -> is_pentagonal (h + x)) low in
	let good = List.filter (fun x -> is_pentagonal (h - x)) sums in
	if List.length good > 0 then
	(h, good)
	else
	search_pentagonal t;;
	let _ =
	let r = search_pentagonal (get_pentagonals 3000) in
	let num = fst(r) in
	let list = snd(r) in
	List.rev_map (fun x -> Printf.printf "%d\n" x) (List.rev_map (fun x -> num - x) list)

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