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 A290977 First n-digit number to appear twice in a row in the decimal expansion of Pi. 2
 3, 59, 209, 9314, 64015, 886287, 7348278 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 209209 and 305305 appear in Pi before any 2-digit number appears twice in a row. a(n) (n >= 1) begins at the following decimal places: 24, 413, 326, 8239, 107472, 1632152, 9719518. - Robert G. Wilson v, Aug 23 2017 LINKS David G. Andersen, The Pi-Search Page. EXAMPLE a(1) = 3 because 3 is the first 1-digit number to appear twice in a row in the decimal expansion of Pi = 3.14159265358979323846264(33)... MATHEMATICA With[{s = Rest@ First@ RealDigits[N[Pi, 10^4]]}, Keys@ Merge[#, Identity] &@ Table[If[Length@ # > 0, TakeSmallest[#, 1], 0 -> 0] &@ Sort[Map[#[[1, 1]] &, DeleteCases[#, {}]]] &@ Map[SequenceCases[#, {a_, b_} /; b == a + n] &, KeyMap[FromDigits, PositionIndex@ Partition[s, n, 1]]], {n, 4}]] (* Michael De Vlieger, Aug 16 2017 *) pi = StringDrop[ ToString[ N[Pi, 1632200]], 2]; f[n_] := Block[{k = 1}, While[ StringTake[pi, {k, k +n -1}] != StringTake[pi, {k +n, k +2n -1}], k++]; k]; Array[f, 6] (* Robert G. Wilson v, Aug 17 2017 *) PROG (PARI) eva(n) = subst(Pol(n), x, 10) pistring(n) = default(realprecision, n+10); my(x=Pi); floor(x*10^n) pidigit(n) = pistring(n)-10*pistring(n-1) consecpidigits(pos, len) = my(v=vector(len)); for(k=1, len, v[k]=pidigit(pos+k)); v a(n) = my(v=[], w=[], x=1); while(1, v=consecpidigits(x, n); w=consecpidigits(x+n, n); if(v==w, return(eva(v))); x++) \\ Felix FrÃ¶hlich, Aug 16 2017 CROSSREFS Cf. A000796, A287994, A290984. Cf. A050279, A096755, A096756, A096757, A096758, A096759, A096760, A096761, A096762, A096763. Sequence in context: A155032 A107212 A002148 * A200957 A057175 A142642 Adjacent sequences:  A290974 A290975 A290976 * A290978 A290979 A290980 KEYWORD base,more,nonn AUTHOR Bobby Jacobs, Aug 16 2017 EXTENSIONS a(6) from Robert G. Wilson v, Aug 19 2017 a(7) from Bobby Jacobs, Aug 22 2017 STATUS approved

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Last modified June 19 13:26 EDT 2019. Contains 324222 sequences. (Running on oeis4.)