A279858 Next term is uniquely the sum of 4 earlier terms.

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

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

Table of n, a(n) for n=1..55.

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 A339507

Adjacent sequences: A279855 A279856 A279857 * A279859 A279860 A279861

Keyword

nonn,easy

Author

Robert G. Wilson v, Dec 20 2016

Status

approved