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A173644 a(n) = smallest positive integer m such that n^2+7m is a square. 0
5, 3, 1, 12, 8, 4, 21, 15, 9, 3, 24, 16, 8, 35, 25, 15, 5, 36, 24, 12, 49, 35, 21, 7, 48, 32, 16, 63, 45, 27, 9, 60, 40, 20, 77, 55, 33, 11, 72, 48, 24, 91, 65, 39, 13, 84, 56, 28, 105, 75, 45, 15, 96, 64, 32, 119, 85, 51, 17, 108, 72, 36, 133, 95, 57, 19, 120, 80, 40, 147, 105, 63, 21, 132, 88, 44, 161, 115, 69, 23, 144, 96, 48, 175, 125, 75, 25, 156, 104, 52, 189, 135, 81, 27, 168, 112, 56, 203, 145 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..99.

FORMULA

Conjecture: a(n)= +2*a(n-7) -a(n-14).

EXAMPLE

n^2+7*a(n) = smallest square:

1^2+7*5=6^2

2^2+7*3=5^2

3^2+7*1=4^2

4^2+7*12=10^2.

MATHEMATICA

Reap[Do[Do[If[IntegerQ[Sqrt[n^2+7m]], Sow[m]; Break[]], {m, 10000}], {n, 200}]][[2, 1]]

CROSSREFS

Sequence in context: A074396 A229958 A157891 * A115991 A143410 A114344

Adjacent sequences:  A173641 A173642 A173643 * A173645 A173646 A173647

KEYWORD

nonn

AUTHOR

Zak Seidov, Dec 05 2010

STATUS

approved

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Last modified February 26 05:51 EST 2020. Contains 332277 sequences. (Running on oeis4.)