This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
a256372 n = a256372_list !! (n-1) a256372_list = [x | x <- [1..], a256210 x == x]
after Robert Israel's Maple program
import Data.IntSet (empty, member, insert)
a256210 n = a256210_list !! (n-1)
a256210_list = 2 : f [2 ..] 2 [1, 3 ..] [4, 6 ..] empty where
f (x:xs) y us'@(u:us) vs'@(v:vs) s
| member x s || u < v = u : f xs u us vs' (insert (y + u) s)
| otherwise = v : f xs v us' vs (insert (y + v) s)
-- Reinhard Zumkeller, Mar 26 2015
N:= 100: # to get a(n) for n <= N
maxodd:= -1:
maxeven:= 2:
a[1]:= 2:
needodd:= {}:
for n from 2 to N do
if member(n,needodd) or maxodd < maxeven then
a[n]:= maxodd + 2;
maxodd:= a[n];
else
a[n]:= maxeven + 2;
maxeven:= a[n];
fi;
needodd:= needodd union {a[n-1]+a[n]};
od:
seq(a[n],n=1..N); # Robert Israel, Mar 26 2015
nn = 100;
maxodd = -1;
maxeven = 2;
a[1] = 2;
needodd = {};
For[n = 2, n <= nn, n++,
If[MemberQ[needodd, n] || maxodd < maxeven,
a[n] = maxodd + 2;
maxodd = a[n]
,
a[n] = maxeven + 2;
maxeven = a[n]
];
needodd = needodd ~Union~ {a[n-1]+a[n]};
];
Array[a, nn] (* Jean-François Alcover, Aug 04 2018, after Robert Israel *)
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