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A001213 a(n) is the solution to the postage stamp problem with n denominations and 3 stamps.

%I A001213 M2647 N1340 #36 Feb 16 2025 08:32:22
%S A001213 3,7,15,24,36,52,70,93,121,154,186,225,271,323,385,450,515,606,684,
%T A001213 788,865,977,1091,1201,1361
%N A001213 a(n) is the solution to the postage stamp problem with n denominations and 3 stamps.
%C A001213 _Fred Lunnon_ [W. F. Lunnon] defines "solution" to be the smallest value not obtainable by the best set of stamps. The solutions given are one lower than this, that is, the sequence gives the largest number obtainable without a break using the best set of stamps.
%D A001213 R. K. Guy, Unsolved Problems in Number Theory, C12.
%D A001213 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D A001213 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A001213 R. Alter and J. A. Barnett, <a href="http://www.jstor.org/stable/2321610">A postage stamp problem</a>, Amer. Math. Monthly, 87 (1980), 206-210.
%H A001213 Erich Friedman, <a href="https://erich-friedman.github.io/mathmagic/0403.html">Postage stamp problem</a>
%H A001213 R. L. Graham and N. J. A. Sloane, <a href="http://dx.doi.org/10.1137/0601045">On Additive Bases and Harmonious Graphs</a>, SIAM J. Algebraic and Discrete Methods, 1 (1980), 382-404.
%H A001213 R. L. Graham and N. J. A. Sloane, <a href="http://neilsloane.com/doc/RLG/073.pdf">On Additive Bases and Harmonious Graphs</a>
%H A001213 W. F. Lunnon, <a href="https://doi.org/10.1093/comjnl/12.4.377">A postage stamp problem</a>, Comput. J. 12 (1969) 377-380.
%H A001213 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PostageStampProblem.html">Postage stamp problem</a>
%Y A001213 Postage stamp sequences: A001208, A001209, A001210, A001211, A001212, A001213, A001214, A001215, A001216, A005342, A005343, A005344, A014616, A053346, A053348, A075060, A084192, A084193.
%Y A001213 A row or column of the array A196416 (possibly with 1 subtracted from it).
%K A001213 nonn,more
%O A001213 1,1
%A A001213 _N. J. A. Sloane_
%E A001213 Entry improved by comments from John Seldon (johnseldon(AT)onetel.com), Sep 15 2004
%E A001213 More terms from _Al Zimmermann_, Feb 20 2002
%E A001213 Further terms from Friedman web site, Jun 20 2003
%E A001213 Incorrect value of a(17) removed by _Al Zimmermann_, Nov 08 2009
%E A001213 a(17)-a(25) from Friedman added by _Robert Price_, Jul 19 2013