This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A138984 #23 Apr 06 2025 18:26:49
%S A138984 1,2,3,9,11,13,23,26,29,43,47,51,69,74,79,101,107,113,139,146,153,183,
%T A138984 191,199,233,242,251,289,299,309,351,362,373,419,431,443,493,506,519,
%U A138984 573,587,601,659,674,689,751,767,783,849,866,883,953,971,989,1063,1082
%N A138984 a(n) = Frobenius number for 4 successive numbers = F(n+1, n+2, n+3, n+4).
%H A138984 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,2,-2,0,-1,1).
%F A138984 G.f.: x*(x^6-4*x^3-x^2-x-1) / ((x-1)^3*(x^2+x+1)^2). [_Colin Barker_, Dec 13 2012]
%F A138984 a(n) = n + (n+1)*floor((n-1)/3). - _Giorgos Kalogeropoulos_, Apr 06 2025
%e A138984 a(4) = 9 because 9 is the largest number k such that the equation 5*x_1 + 6*x_2 + 7*x_3 + 9*x_4 = k has no solution for any nonnegative x_i (in other words, for every k > 9 there exist one or more solutions).
%t A138984 Table[FrobeniusNumber[{n + 1, n + 2, n + 3, n + 4}], {n, 1, 100}]
%t A138984 Table[n + Floor[(n-1)/3]*(n+1), {n,56}] (* _Giorgos Kalogeropoulos_, Apr 06 2025 *)
%Y A138984 Frobenius number for k successive numbers: A028387 (k=2), A079326 (k=3), this sequence (k=4), A138985 (k=5), A138986 (k=6), A138987 (k=7), A138988 (k=8).
%K A138984 nonn,easy
%O A138984 1,2
%A A138984 _Artur Jasinski_, Apr 05 2008