This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A209493 #19 Nov 04 2024 09:30:41
%S A209493 2,5,11,17,61,103,167,193,293,643,647,911,11243,29437,55021,80141
%N A209493 Indices of primes in sequence A006190.
%C A209493 Index must be prime. The indices greater than 293 yield probable primes.
%t A209493 seq=RecurrenceTable[{a[n]==3*a[n-1]+a[n-2], a[1]==1, a[2]==3}, a, {n, 1000}]; Select[Range[1000], PrimeQ[seq[[#]]]&]
%Y A209493 Cf. A006190, A006497, A000129, A096650.
%K A209493 nonn,hard,more
%O A209493 1,1
%A A209493 _Vaclav Kotesovec_, Mar 09 2012
%E A209493 a(14)-a(15) from _Vaclav Kotesovec_, Sep 08 2013
%E A209493 a(16) from _Michael S. Branicky_, Nov 03 2024