

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
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OFFSET

1,2


COMMENTS

Note that a(22) = 163 is the last prime generated by this sequence. All subsequent terms are composite and equal (16n)(n+17)/2.


LINKS

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


FORMULA

a(n) = (n16)(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) = 64 = 2 etc.


MATHEMATICA

a=3; Join[{1, 3}, Table[If[PrimeQ[a], a=a+n, a=an], {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



