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 A180446 Number of non-pentagonal numbers <= n. 3
 0, 0, 1, 2, 3, 3, 4, 5, 6, 7, 8, 9, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 63, 64, 65, 66 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 LINKS Harvey P. Dale, Table of n, a(n) for n = 0..1000 FORMULA a(n) = n - floor((sqrt(24n+1)+1)/6) = n - A180447(n). EXAMPLE a(5) = 5 - floor((sqrt(24*5+1)+1)/6) = 3. MATHEMATICA f[n_] := n - Floor[(Sqrt[24 n + 1] + 1)/6]; Array[f, 74, 0] (* Robert G. Wilson v, Sep 10 2010 *) Accumulate[Table[If[IntegerQ[(1+Sqrt[1+24n])/6], 0, 1], {n, 0, 80}]]-1 (* Harvey P. Dale, May 22 2023 *) PROG (Python) l = [n-floor((sqrt(24*n+1)+1)/6) for n in range(0, 101)] CROSSREFS Sequence in context: A108789 A091960 A162621 * A095394 A257682 A029928 Adjacent sequences: A180443 A180444 A180445 * A180447 A180448 A180449 KEYWORD easy,nonn AUTHOR William A. Tedeschi, Sep 07 2010 EXTENSIONS More terms from Robert G. Wilson v, Sep 10 2010 STATUS approved

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Last modified August 7 14:45 EDT 2024. Contains 375012 sequences. (Running on oeis4.)