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 A059868 There exist no palindromic pentagonals of length a(n). 7
 3, 9, 11, 12, 24 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS P. De Geest, Palindromic pentagonals MATHEMATICA A002069 = {0, 1, 5, 22, 1001, 2882, 15251, 720027, 7081807, 7451547, 26811862, 54177145, 1050660501, 1085885801, 1528888251, 2911771192, 2376574756732, 5792526252975, 5875432345785, 10810300301801, 264571020175462, 5292834004382925, 10808388588380801, 15017579397571051, 76318361016381367, 150621384483126051, 735960334433069537, 1003806742476083001, 1087959810189597801, 2716280733370826172}; A059868[n_] := Length[Select[A002069, IntegerLength[#] == n  || (n == 1 && # == 0) &]]; Select[Range[18], A059868[#] == 0 &] (* Robert Price, Apr 26 2019 *) CROSSREFS Cf. A034822, A059869, A059870, A034307, A000326, A028386, A002069. Sequence in context: A070354 A174565 A074261 * A101735 A101620 A235583 Adjacent sequences:  A059865 A059866 A059867 * A059869 A059870 A059871 KEYWORD nonn,base,hard AUTHOR Patrick De Geest, Feb 15 2000 EXTENSIONS Name clarified by David A. Corneth, Apr 26 2019 STATUS approved

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Last modified October 16 16:18 EDT 2019. Contains 328101 sequences. (Running on oeis4.)