A138790 - OEIS

A138790

a(n) = indices n for which A138793(n) is prime.

61, 946

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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

Table of n, a(n) for n=1..2.

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