OFFSET
1,1
COMMENTS
Index must be prime. The indices greater than 293 yield probable primes.
MATHEMATICA
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[[#]]]&]
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Vaclav Kotesovec, Mar 09 2012
EXTENSIONS
a(14)-a(15) from Vaclav Kotesovec, Sep 08 2013
STATUS
approved