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 A285767 Cyclops octagonal numbers: a(n) = n*(3*n-2) with one "zero" digit in the middle. 0
 0, 408, 11041, 18096, 22016, 23056, 28033, 38081, 56033, 61061, 1140833, 1170625, 1250656, 1410416, 1460216, 1540833, 2120161, 2130261, 2140385, 2150533, 2310896, 2390561, 2460696, 2520833, 2570576, 2780181, 2920533, 3230256, 3280256, 3490565, 3660865, 3680776 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The n-th octagonal number x(n) = n*(3*n - 2). Subset of A000567. All the terms have the number of digits odd with only one "zero" digit in the middle. LINKS Table of n, a(n) for n=1..32. EXAMPLE For n = 12; x(12) = 12*(3*12 - 2) = 408 that is 12th octagonal number with one zero digit in the middle, hence appears in the sequence. For n = 61; x(61) = 61*(3*61 - 2) = 11041 that is 61st octagonal number with one zero digit in the middle, hence appears in the sequence. MAPLE iscyclops:= proc(n) local L, t; t:= ilog10(n); if t::odd then return false fi; L:= convert(n, base, 10); L[1+t/2] = 0 and numboccur(0, L) = 1 end proc: iscyclops(0):= true: select(iscyclops, [seq(n*(3*n-2), n=0..1000)]); MATHEMATICA Select[Table[n (3 n - 2), {n, 0, 1110}], And[OddQ@ Length@ #, Count[#, 0] == 1, Take[#, {Ceiling[Length[#]/2]}] == {0}] &@ IntegerDigits@ # &] (* Michael De Vlieger, Apr 26 2017 *) CROSSREFS Intersection of A000567 and A134808. Cf. A000567, A134808, A134809, A160717. Sequence in context: A234697 A337795 A183717 * A282479 A163024 A283948 Adjacent sequences: A285764 A285765 A285766 * A285768 A285769 A285770 KEYWORD nonn,base AUTHOR K. D. Bajpai, Apr 25 2017 STATUS approved

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Last modified July 18 01:34 EDT 2024. Contains 374377 sequences. (Running on oeis4.)