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%I #26 Mar 29 2024 14:36:00
%S 1,3,9,15,39,225,231,363,687,1299,1335,1809,2367,12735
%N Indices of primes in sequence A108300.
%C Conjecture: for n>1 a(n) is a multiple of 3.
%C The indices greater than 363 yield probable primes. - _Vaclav Kotesovec_, Oct 28 2013
%C Next term > 100000. - _Tyler Busby_, Mar 29 2024
%t seq=RecurrenceTable[{a[n]==3*a[n-1]+a[n-2],a[0]==1,a[1]==5},a,{n,1,1000}]; Select[Range[1000],PrimeQ[seq[[#]]]&]
%Y Cf. A108300, A209493, A001605, A001606, A096650, A099088.
%K nonn,hard,more
%O 1,2
%A _Vaclav Kotesovec_, Sep 08 2013