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 A279858 Next term is uniquely the sum of 4 earlier terms. 0
 1, 2, 4, 8, 15, 22, 26, 28, 36, 37, 41, 98, 117, 120, 124, 214, 222, 226, 236, 333, 338, 532, 533, 534, 538, 541, 543, 544, 743, 746, 956, 957, 958, 961, 1054, 1263, 1267, 1463, 1466, 1468, 1473, 1474, 1475, 1476, 1684, 1894, 2196, 2198, 2199, 2205, 2206, 2404, 2406, 2408, 2411 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 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. Written this way, we see that this sequence is to 4 as A007087 is to 3 and A002858 (Ulam numbers) is to 2. LINKS MATHEMATICA 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 *) CROSSREFS Cf. A002858, A007086, A007087. Sequence in context: A290652 A288313 A213020 * A026474 A301629 A305992 Adjacent sequences:  A279855 A279856 A279857 * A279859 A279860 A279861 KEYWORD nonn,easy AUTHOR Robert G. Wilson v, Dec 20 2016 STATUS approved

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Last modified December 4 09:10 EST 2020. Contains 338921 sequences. (Running on oeis4.)