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.
import Data.Set (Set, singleton, notMember, insert)
a057165 n = a057165_list !! n
a057165_list = r (singleton 0) 1 0 where
r :: Set Integer -> Integer -> Integer -> [Integer]
r s n x = if x > n && (x - n) `notMember` s
then r (insert (x-n) s) (n+1) (x-n)
else n : r (insert (x+n) s) (n+1) (x+n)
-- Reinhard Zumkeller, Mar 17 2011
h := array(1..100000); maxt := 100000; a := array(1..1000); a[1] := 1; h[1] := 1; for nx from 2 to 1000 do t1 := a[nx-1]-nx; if t1>0 and h[t1] <> 1 then a[nx] := t1; if t1 < maxt then h[t1] := 1; fi; else for i from 0 to 1000 do t1 := a[nx-1]+nx+i; if h[t1] <> 1 then a[nx] := t1; if t1 < maxt then h[t1] := 1; fi; break; fi; od; fi; od; evalm(a);
a(5) = 19: A005132(19-1) = 43 and 43-19>0, but the term 24=43-19 is already in A005132, therefore A005132(19)=43+19=62; A187943(5)=15 and A005132(15)=24.
import Data.Set (Set, singleton, member, insert)
a187922 n = a187922_list !! (n-1)
a187922_list = r (singleton 0) 1 0 where
r :: Set Integer -> Integer -> Integer -> [Integer]
r s n x | x <= n = r (insert (x+n) s) (n+1) (x+n)
| (x-n) `member` s = n : r (insert (x+n) s) (n+1) (x+n)
| otherwise = r (insert (x-n) s) (n+1) (x-n)
(C++) See Links section.
Start with 1 from A, add 2 from A getting 3, subtract 1 from B getting 2, add 3 from A getting 5, add 4 from A getting 9, subtract 5 from A getting 4, add 6 from A getting 10, subtract 2 from B getting 8, add 7 from A getting 15, add 9 from A getting 16, subtract 10 from A getting 6, add 11 from A getting 17, subtract 3 from B getting 14, add 12 from A getting 26, subtract 13 from A getting 13, ...
rem Chipmunk BASIC v3.6.4(b8) http://www.nicholson.com/rhn/basic/ max=1000 : dim a(max) s=2 : z=1 : a(z)=1 : print str$(z)+","; for n=1 to 200 x=z-s : if x <= 0 then goto yyy if a(x)=0 then a(x)=1 : print str$(x)+","; : s=s+1 : z=x : goto xxx yyy: for i=0 to max x=z+s+i if a(x)=0 then a(x)=1 : print str$(x)+","; : s=s+i+1 : z=x : goto xxx next i xxx: next n print : end rem Jeremy Gardiner, Feb 22 2014
a(10)=26: A005132(26-1) = 17 and 17-26<0, hence A005132(26) = 17+26 = 43.
import Data.Set (Set, singleton, member, insert)
a187921 n = a187921_list !! (n-1)
a187921_list = r (singleton 0) 1 0 where
r :: Set Integer -> Integer -> Integer -> [Integer]
r s n x | x <= n = n : r (insert (x+n) s) (n+1) (x+n)
| (x-n) `member` s = r (insert (x+n) s) (n+1) (x+n)
| otherwise = r (insert (x-n) s) (n+1) (x-n)
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