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%I #13 Dec 24 2016 13:11:31
%S 1,2,4,8,15,22,26,28,36,37,41,98,117,120,124,214,222,226,236,333,338,
%T 532,533,534,538,541,543,544,743,746,956,957,958,961,1054,1263,1267,
%U 1463,1466,1468,1473,1474,1475,1476,1684,1894,2196,2198,2199,2205,2206,2404,2406,2408,2411
%N Next term is uniquely the sum of 4 earlier terms.
%C With a(1)=1, a(2)=2, a(3)=4, a(4)=8 and for n>4, a(n) = least number which is a unique sum of four distinct earlier terms.
%C Written this way, we see that this sequence is to 4 as A007087 is to 3 and A002858 (Ulam numbers) is to 2.
%t a[n_ /; n <= 4] := 2^(n - 1); a[n_] := a[n] = (t = Table[a[i] + a[j] + a[k] + a[l], {i, 1, n - 4}, {j, i + 1, n - 3}, {k, j + 1, n - 2}, {l, k + 1, n - 1}] // Flatten; Complement[ Select[t // Tally, #[[2]] == 1 &][[All, 1]], Array[a, n - 1]] // Sort // First); Array[a, 55] (* after _Jean-François Alcover_ A007086 *)
%Y Cf. A002858, A007086, A007087.
%K nonn,easy
%O 1,2
%A _Robert G. Wilson v_, Dec 20 2016
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