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 A020331 Numbers n such that base 3 representation is the juxtaposition of two identical strings. 6
 4, 8, 30, 40, 50, 60, 70, 80, 252, 280, 308, 336, 364, 392, 420, 448, 476, 504, 532, 560, 588, 616, 644, 672, 700, 728, 2214, 2296, 2378, 2460, 2542, 2624, 2706, 2788, 2870, 2952, 3034, 3116, 3198, 3280, 3362, 3444, 3526, 3608, 3690, 3772, 3854, 3936, 4018 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS FORMULA a(n) = n*3^floor(log_3(n)+1) + n. - Ilya Gutkovskiy, Jan 26 2018 MATHEMATICA b3iQ[n_]:=Module[{idn3=IntegerDigits[n, 3], len}, len=Length[idn3]; EvenQ[ len] && Take[idn3, len/2]==Take[idn3, -len/2 ]]; Select[Range[5000], b3iQ] (* Harvey P. Dale, Feb 08 2015 *) CROSSREFS Cf. A020330, A020332, A020333, A020334, A020335, A020336, A020337, A020338. Sequence in context: A256456 A270522 A317583 * A248476 A082595 A262154 Adjacent sequences:  A020328 A020329 A020330 * A020332 A020333 A020334 KEYWORD nonn,base AUTHOR David W. Wilson, Melia Aldridge, ma38(AT)spruce.evansville.edu STATUS approved

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Last modified October 14 04:44 EDT 2019. Contains 327995 sequences. (Running on oeis4.)