The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A323047 Numbers that are not the sum of three (or fewer) 3-smooth numbers. 2
 431, 485, 509, 565, 637, 671, 719, 725, 727, 862, 887, 935, 941, 943, 959, 967, 970, 1130, 1151, 1175, 1199, 1205, 1274, 1293, 1319, 1342, 1367, 1373, 1391, 1415, 1421, 1423, 1438, 1439, 1445, 1447, 1450, 1453, 1454, 1455, 1481, 1527, 1535, 1559 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers below 431 may be written as a sum of three (or fewer) elements in A003586. These are the first exceptions. Below 18431 every number can be written as a sum of 4 or fewer 3-smooth numbers, and below 3448733 every number can be written as a sum of 5 or fewer 3-smooth numbers (cf. sequence A018899). LINKS Robert Israel, Table of n, a(n) for n = 1..10000 MAPLE N:= 1000: # for all terms <= N S:= {seq(seq(2^i*3^j, i=0..ilog2(N/3^j)), j=0..floor(log[3](N)))}: S2:= select(`<=`, map(t -> op(map(`+`, S, t)), S), N): S3:= select(`<=`, map(t -> op(map(`+`, S, t)), S2), N): A:= {\$1..N} minus S minus S2 minus S3: sort(convert(A, list)); # Robert Israel, May 19 2019 MATHEMATICA f[n_] := Union@ Flatten@ Table[2^a * 3^b, {a, 0, Log2[n]}, {b, 0, Log[3, n/2^a]}]; b=Block[{nn = 2000, s}, s = f[nn]; {0, 1, 2}~Join~Select[Union@ Flatten@ Outer[Plus, s, s, s], # <= nn &]]; Complement[Range[2000], b] CROSSREFS Cf. A003586, A018899, A237442, A323046, A323048, A323049, A323050. Sequence in context: A176387 A160518 A273807 * A046018 A142802 A003548 Adjacent sequences:  A323044 A323045 A323046 * A323048 A323049 A323050 KEYWORD nonn AUTHOR Carlos Alves, Jan 03 2019 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 2 12:01 EST 2021. Contains 349440 sequences. (Running on oeis4.)