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A047739 Economical palindromes. 0

%I

%S 343,1331,10201,14641,31213,94249,1030301,1332331,1367631,1478741,

%T 2060602,2513152,2551552,2570752,2939392,2977792,3090903,3498943,

%U 3637363,3735373,3850583,5221225,5265625,5734375,6948496,11288211,11333311,12100121,12499421,13577531,14655641,22666622,27700772,29399392,31244213,33999933,38988983,58344385,71111117,100020001,100585001,101000101,104060401,104555401,106878601

%N Economical palindromes.

%e 343 = 7^3; 3 digits in 343, 2 digits in 7^3, so 343 is economical.

%t d[n_]:=IntegerDigits[n]; palQ[n_]:=Reverse[(x=d[n])]==x; ecQ[n_]:=Length[Flatten[d[{First/@(x=FactorInteger[n]), DeleteCases[Last/@x,1]}]]] < Length[d[n]]; t={}; Do[If[palQ[n] && ecQ[n], AppendTo[t,n]], {n,3860000}]; t (* _Jayanta Basu_, May 16 2013 *)

%Y Cf. A046759.

%K nonn,base

%O 1,1

%A _Carlos Rivera_

%E a(11)-a(45) from _Donovan Johnson_, Nov 24 2010

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Last modified August 20 22:45 EDT 2019. Contains 326155 sequences. (Running on oeis4.)