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A117128
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Recaman transform of primes (another version): a(0)=1; for n>0, a(n) = a(n-1) - prime(n) if that number is positive and not already in the sequence, otherwise a(n) = a(n-1) + prime(n).
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5
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1, 3, 6, 11, 4, 15, 2, 19, 38, 61, 32, 63, 26, 67, 24, 71, 18, 77, 16, 83, 12, 85, 164, 81, 170, 73, 174, 277, 384, 275, 162, 35, 166, 29, 168, 317, 468, 311, 148, 315, 142, 321, 140, 331, 138, 335, 136, 347, 124, 351, 122, 355, 116, 357, 106, 363, 100, 369, 98, 375, 94, 377
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OFFSET
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0,2
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COMMENTS
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Equals A064365(n) - 1. Differs from Cald's sequence A006509 for first time at n=116 (or 117, depending on offset).
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LINKS
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_Reinhard Zumkeller_, Table of n, a(n) for n = 0..10000
Index entries for sequences related to Recaman's sequence
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MAPLE
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M1:=500000; a:=array(0..M1); have:=array(1..M1); a[0]:=1; for n from 1 to M1 do have[n]:=0; od: have[1]:=1;
M2:=2000; nmax:=M2;
for n from 1 to M2 do p:=ithprime(n); i:=a[n-1]-p; j:=a[n-1]+p;
if i >= 1 and have[i]=0 then a[n]:=i; have[i]:=1;
elif j <= M1 then a[n]:=j; have[j]:=1;
else nmax:=n-1; break; fi; od: [seq(a[n], n=0..M2)];
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PROG
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(Haskell)
import Data.Set (singleton, notMember, insert)
a117128 n = a117128_list !! n
a117128_list = 1 : f 1 a000040_list (singleton 1) where
f x (p:ps) s | x' > 0 && x' `notMember` s = x' : f x' ps (insert x' s)
| otherwise = xp : f xp ps (insert xp s)
where x' = x - p; xp = x + p
-- Reinhard Zumkeller, Apr 26 2012
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CROSSREFS
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Cf. A064365, A006509, A112877.
Sequence in context: A083462 A110080 A093903 * A006509 A144562 A102889
Adjacent sequences: A117125 A117126 A117127 * A117129 A117130 A117131
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane, Apr 20 2006
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STATUS
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approved
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