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A175117 Numbers n such that Sum_(i=1..n) p(i)*(-1)^(i+1) = c^2. p(i) i-th prime,c an integer. 1
3, 9, 55, 181, 215, 459, 1361, 1417, 1623, 2047, 2445, 4685, 6687, 7353, 7785, 7925, 8489, 10333, 10515, 11179, 14087, 15227, 15829 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that (-1)^n*A008347(n) is a perfect square. [From R. J. Mathar, Feb 21 2010]

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..300

EXAMPLE

2-3+5=4 thus a(1)=3 2-3+5-7+11-13+17-19+23=16 thus a(2)=9

MATHEMATICA

Flatten[Position[Accumulate[Times@@@Partition[Riffle[Prime[Range[ 20000]], {1, -1}, {2, -1, 2}], 2]], _?(IntegerQ[Sqrt[#]]&)]] (* Harvey P. Dale, Mar 19 2013 *)

CROSSREFS

A000040

Sequence in context: A001194 A032179 A233189 * A245117 A183303 A075979

Adjacent sequences:  A175114 A175115 A175116 * A175118 A175119 A175120

KEYWORD

easy,nonn

AUTHOR

Ctibor O. Zizka, Feb 14 2010

EXTENSIONS

Six more terms from R. J. Mathar, Feb 21 2010

STATUS

approved

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Last modified May 27 13:00 EDT 2020. Contains 334657 sequences. (Running on oeis4.)