cp's OEIS Frontend

A006638 Restricted postage stamp problem with n denominations and 2 stamps.

%I A006638 M1088 #34 Jul 08 2025 16:51:03
%S A006638 2,4,8,12,16,20,26,32,40,44,54,64,72,80,92,104,116,128,140,152,164,
%T A006638 180,196,212,228,244,262,280,298,316,338,360,382,404,426,448,470,492,
%U A006638 514,536,562,588,614,644,674,704,734
%N A006638 Restricted postage stamp problem with n denominations and 2 stamps.
%C A006638 a(n) = largest span (range) attained by a restricted additive 2-basis of length n; an additive 2-basis is restricted if its span is exactly twice its largest element. - _Jukka Kohonen_, Apr 23 2014
%D A006638 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A006638 J. Kohonen, <a href="http://cs.uwaterloo.ca/journals/JIS/VOL17/Kohonen2/kohonen5.html">A Meet-in-the-Middle Algorithm for Finding Extremal Restricted Additive 2-Bases</a>, J. Integer Seq., 17 (2014), Article 14.6.8.
%H A006638 J. Kohonen, <a href="http://arxiv.org/abs/1503.03416">Early Pruning in the Restricted Postage Stamp Problem</a>, arXiv:1503.03416 [math.NT] preprint (2015).
%H A006638 S. S. Wagstaff, Jr., <a href="http://dx.doi.org/10.1007/BFb0062717">Additive h-bases for n</a>, pp. 302-327 of Number Theory Carbondale 1979, Lect. Notes Math. 751 (1982).
%e A006638 a(10)=44: For example, the basis {0, 1, 2, 3, 7, 11, 15, 17, 20, 21, 22} has 10 nonzero elements, and all integers between 0 and 44 can be expressed as sums of two elements of the basis. Currently n=10 is the only known case where A006638 differs from A001212. - _Jukka Kohonen_, Apr 23 2014
%Y A006638 Cf. A001212.
%K A006638 nonn
%O A006638 1,1
%A A006638 _N. J. A. Sloane_
%E A006638 Definition improved by _Jukka Kohonen_, Apr 23 2014
%E A006638 Extended up to a(41) from Kohonen (2014), by _Jukka Kohonen_, Apr 23 2014
%E A006638 Extended up to a(47) from Kohonen (2015), by _Jukka Kohonen_, Mar 14 2015