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%I #9 Dec 15 2017 17:36:00
%S 1,3,6,2,7,13,20,12,3,13,24,12,-1,-15,-30,-46,-63,-81,-100,-120,-141,
%T -163,-140,-164,-189,-215,-242,-270,-299,-329,-360,-392,-425,-459,
%U -494,-530,-567,-605,-644,-684,-725,-767,-810,-854,-899,-945,-992,-1040,-1089,-1139,-1190,-1242,-1295,-1349,-1404,-1460
%N Start with 1, add the next number if one gets a prime then add the next number else subtract the next...
%C Note that a(22) = -163 is the last prime generated by this sequence. All subsequent terms are composite and equal (16-n)(n+17)/2.
%F a(n) = -(n-16)(n+17)/2 for n > 22
%e a(1) = 1, a(2) = 1+2 =3 is a prime hence a(3) = 3 +3 = 6 which is composite hence a(4) = 6-4 = 2 etc.
%t a=3; Join[{1, 3}, Table[If[PrimeQ[a], a=a+n, a=a-n], {n, 3, 60}]]
%Y Cf. A074171.
%K easy,sign
%O 1,2
%A _Amarnath Murthy_, Aug 30 2002
%E Corrected and extended by _Jason Earls_, Sep 01 2002
%E Corrected by _T. D. Noe_, Oct 04 2004
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