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 A022440 a(n) = c(n-1) + c(n-3) where c is the sequence of positive numbers not in a. 2
 3, 4, 5, 7, 10, 15, 19, 21, 24, 26, 29, 31, 34, 37, 40, 43, 47, 50, 53, 57, 60, 63, 67, 69, 73, 75, 79, 81, 85, 87, 90, 93, 95, 99, 101, 105, 107, 110, 113, 115, 119, 121, 125, 127, 130, 133, 136, 139, 142, 145, 148, 151, 154, 157, 160, 163, 166, 169, 172, 175, 179, 181 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS From N. J. A. Sloane, Nov 24 2004: I'm not sure of the minimal hypotheses needed to generate this sequence, but one method that works is the following: Start with a(1)=3, a(2)=4, a(3)=5, so that we know c(1)=1 and c(2)=2. Let c(3) = x >= 6, so that a(4) = 1+x >= 6 and x=6 is forced, with a(4)=7. Then c(4) >= 8, a(5) >= 10, so definitely c(4)=8 and c(5)=9. From now on the sequence extends easily. LINKS G. C. Greubel, Table of n, a(n) for n = 1..10000 MATHEMATICA Fold[Append[#1, Plus @@ Complement[Range[Max@#1 + 3], #1][[{#2, #2 + 2}]]] &, {3, 4, 5}, Range[59]] (* Ivan Neretin, Mar 30 2017 *) CROSSREFS Cf. A022424 and references therein. Sequence in context: A309916 A162311 A003312 * A088130 A046840 A057773 Adjacent sequences:  A022437 A022438 A022439 * A022441 A022442 A022443 KEYWORD nonn,easy AUTHOR EXTENSIONS More terms from Jon E. Schoenfield, Apr 02 2010 STATUS approved

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Last modified September 20 10:49 EDT 2020. Contains 337264 sequences. (Running on oeis4.)