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 A074170 Start with 1, add the next number if one gets a prime then add the next number else subtract the next... 3
 1, 3, 6, 2, 7, 13, 20, 12, 3, 13, 24, 12, -1, -15, -30, -46, -63, -81, -100, -120, -141, -163, -140, -164, -189, -215, -242, -270, -299, -329, -360, -392, -425, -459, -494, -530, -567, -605, -644, -684, -725, -767, -810, -854, -899, -945, -992, -1040, -1089, -1139, -1190, -1242, -1295, -1349, -1404, -1460 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 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. LINKS FORMULA a(n) = -(n-16)(n+17)/2 for n > 22 EXAMPLE 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. MATHEMATICA a=3; Join[{1, 3}, Table[If[PrimeQ[a], a=a+n, a=a-n], {n, 3, 60}]] CROSSREFS Cf. A074171. Sequence in context: A273465 A125717 A065232 * A076543 A274648 A277558 Adjacent sequences:  A074167 A074168 A074169 * A074171 A074172 A074173 KEYWORD easy,sign AUTHOR Amarnath Murthy, Aug 30 2002 EXTENSIONS Corrected and extended by Jason Earls, Sep 01 2002 Corrected by T. D. Noe, Oct 04 2004 STATUS approved

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Last modified November 17 19:15 EST 2018. Contains 317276 sequences. (Running on oeis4.)