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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

Table of n, a(n) for n=1..56.

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.)