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 A033691 Minimal number of vertices in 1-1 deficient regular graph where minimal degree is 1 and maximal degree is n. 2
 4, 8, 12, 20, 24, 32, 40, 52, 60, 72, 84, 100, 112, 128, 144, 164, 180, 200, 220, 244, 264, 288, 312, 340, 364, 392, 420, 452, 480, 512, 544, 580, 612, 648, 684, 724, 760, 800, 840, 884, 924, 968, 1012, 1060, 1104, 1152, 1200, 1252, 1300, 1352, 1404, 1460 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS A 1-1 deficient regular graph is one in which every vertex has the same degree as all of its neighbors except exactly one and its degree differs from the degree of this neighbor by exactly 1. LINKS Vincenzo Librandi, Table of n, a(n) for n = 2..1000 FORMULA a(2*i) = 2*i*(i+1) i=1, 2, 3, ...; a(4*i+3) = 2*(i+1)*(4*i+4) i=0, 1, 2, ...; a(4*i+5) = 4*(2*i^2+6*i+5) i=1, 2, 3, ... Empirical G.f.: -4*x^2*(x^5-2*x^4+x^3+1) / ((x-1)^3*(x+1)*(x^2+1)). [Colin Barker, Jan 15 2013] MATHEMATICA a[n_?EvenQ] := n*(n+2)/2; a[n_ /; Mod[n, 4] == 3] := (n+1)^2/2; a[n_ /; Mod[n, 4] == 1] := (n^2 + 2*n + 5)/2; Table[a[n], {n, 2, 53}] (* Jean-François Alcover, Oct 10 2011 *) CROSSREFS Sequence in context: A311655 A311656 A311657 * A090658 A268799 A269711 Adjacent sequences:  A033688 A033689 A033690 * A033692 A033693 A033694 KEYWORD easy,nice,nonn AUTHOR Lisa R. Macon (lmacon(AT)valencia.cc.fl.us) EXTENSIONS More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Mar 23 2003 STATUS approved

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Last modified July 13 03:03 EDT 2020. Contains 335673 sequences. (Running on oeis4.)