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 A090467 Numbers which are not regular figurative or polygonal numbers of order greater than 2. That is, numbers not of the form 1 + k*n(n-1)/2 - (n-1)^2 where n >= 2 and k >= 2. 4
 1, 2, 3, 4, 5, 7, 8, 11, 13, 14, 17, 19, 20, 23, 26, 29, 31, 32, 37, 38, 41, 43, 44, 47, 50, 53, 56, 59, 61, 62, 67, 68, 71, 73, 74, 77, 79, 80, 83, 86, 89, 97, 98, 101, 103, 104, 107, 109, 110, 113, 116, 119, 122, 127, 128, 131, 134, 137, 139, 140, 143, 146, 149, 151, 152 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The n-th k-gonal number is 1 + k*n(n-1)/2 - (n-1)^2 = A057145(k,n). REFERENCES Albert H. Beiler, Recreations In The Theory Of Numbers, The Queen Of Mathematics Entertains, Dover, NY, 1964, pp. 185-199. LINKS T. D. Noe, Table of n, a(n) for n=1..1000 Eric Weisstein's World of Mathematics, Figurate Number. FORMULA An integer n >= 3 is in this sequence iff A176774(n) = n (or, equivalently, A176775(n) = 2). - Max Alekseyev, Apr 24 2018 MATHEMATICA Complement[ Table[i, {i, 300}], Take[ Union[ Flatten[ Table[1 + k*n(n - 1)/2 - (n - 1)^2, {n, 3, 40}, {k, 3, 300}]]], 300]] PROG (PARI) isok(n) = (n < 3) || (vecsum(vector(n-2, k, k+=2; ispolygonal(n, k))) == 1); \\ Michel Marcus, May 01 2016 CROSSREFS Complement is A090466. Sequence in context: A062890 A259626 A058586 * A177202 A053868 A241912 Adjacent sequences:  A090464 A090465 A090466 * A090468 A090469 A090470 KEYWORD easy,nonn AUTHOR Robert G. Wilson v, Dec 01 2003 EXTENSIONS Verified by Don Reble, Mar 12 2006 STATUS approved

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Last modified September 21 04:59 EDT 2019. Contains 327253 sequences. (Running on oeis4.)