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 A138790 a(n) = indices n for which A138793(n) is prime. 17
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 OFFSET 1,1 COMMENTS Indices where number 1 occured in A138789. There are no more primes for n<=5000. a(3) > 20000. - Robert Price, Mar 24 2015 LINKS EXAMPLE a(1) = 61 because the number 160695...654321 is prime. MATHEMATICA b = {}; a = {}; Do[w = RealDigits[n]; w = First[w]; Do[AppendTo[a, w[[k]]], {k, 1, Length[w]}]; p = FromDigits[Reverse[a]]; If[PrimeQ[p], Print[n]; AppendTo[b, p]], {n, 1, 2000}]; b (* Artur Jasinski, Mar 30 2008 *) Select[Range[1, 1000], PrimeQ[lst = {}; Do[lst = Join[lst, IntegerDigits[n]], {n, 1, #}]; FromDigits[Reverse[lst]]] &] (* Robert Price, Mar 24 2015 *) CROSSREFS Cf. A000422, A116504, A007908, A116505, A138793, A138789. Sequence in context: A008358 A317283 A264306 * A057534 A152868 A218112 Adjacent sequences:  A138787 A138788 A138789 * A138791 A138792 A138793 KEYWORD nonn,bref,hard,more,base AUTHOR Artur Jasinski, Mar 30 2008, Mar 31 2008 STATUS approved

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Last modified August 19 08:26 EDT 2019. Contains 326115 sequences. (Running on oeis4.)