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 A020656 Lexicographically earliest increasing sequence of nonnegative numbers that contains no arithmetic progression of length 6. 28
 0, 1, 2, 3, 4, 6, 7, 8, 9, 11, 12, 13, 14, 16, 17, 18, 19, 21, 22, 23, 24, 25, 32, 33, 34, 35, 36, 38, 42, 43, 44, 45, 46, 48, 49, 50, 51, 58, 59, 61, 62, 63, 64, 65, 67, 68, 70, 72, 76, 84, 86, 87, 88, 89, 90, 92, 95, 96, 97, 98, 99, 102, 103, 106, 110, 113, 114, 116, 117, 119, 121 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS David W. Wilson, Table of n, a(n) for n = 1..10000 FORMULA a(n) = A005838(n) - 1. EXAMPLE 5 is excluded since (0,1,2,3,4,5) would be a 6-term AP. 10 is excluded since (0,2,4,6,8,10) would be a 6-term AP. Idem for 15 and 20. 25 is not excluded, but after 25 (1,6,11,16,21,26) would be a 6-AP, and similarly all of 26 through 32 are excluded. PROG (PARI) A020656(n, show=1, i=0, o=6, u=0)={for(n=1, n, show&&print1(i, ", "); u+=1<=0), A003278 (>0); 4-term AP: A005839 (>=0), A005837 (>0); 5-term AP: A020654 (>=0), A020655 (>0); 6-term AP: A020656 (>=0), A005838 (>0); 7-term AP: A020657 (>=0), A020658 (>0); 8-term AP: A020659 (>=0), A020660 (>0); 9-term AP: A020661 (>=0), A020662 (>0); 10-term AP: A020663 (>=0), A020664 (>0). Sequence in context: A045774 A045681 A001961 * A039116 A047201 A225496 Adjacent sequences:  A020653 A020654 A020655 * A020657 A020658 A020659 KEYWORD nonn AUTHOR EXTENSIONS Edited by M. F. Hasler, Jan 03 2016 Further edited (with new offset) by N. J. A. Sloane, Jan 04 2016 STATUS approved

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Last modified October 18 02:23 EDT 2019. Contains 328135 sequences. (Running on oeis4.)