A173644 a(n) = smallest positive integer m such that n^2+7m is a square.

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

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 A352136 A143410

Adjacent sequences: A173641 A173642 A173643 * A173645 A173646 A173647

Keyword

nonn

Author

Zak Seidov, Dec 05 2010

Status

approved