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 A285885 Ulam numbers n such that 3*n is also an Ulam number. 3
 1, 2, 6, 16, 38, 138, 182, 209, 309, 341, 612, 1030, 1389, 2513, 2584, 2628, 2650, 2750, 3031, 3207, 3290, 3593, 3742, 3874, 3962, 4121, 4155, 4998, 5384, 5797, 6552, 6723, 6833, 7461, 7979, 8453, 8541, 8844, 8949, 9015, 9164, 9577, 10547, 10569, 11197, 11346 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS It appears that there are many more values in this sequence than in A068791, Ulam numbers n such that 2*n is also an Ulam number. LINKS Robert Israel, Table of n, a(n) for n = 1..1570 MAPLE N:= 40000: # for terms <= N/3 V:= Vector(N): U:= [1, 2]: V[3]:= 1: for i from 3 do found:= false; for j from U[i-1]+1 to N do if V[j]=1 then found:= true; break fi od; if not found then break fi; R:= select(`<=`, j+~U, N): V[R]:= 1 +~ V[R]; U:= [op(U), j]; od: U:= convert(U, set): sort(convert(U intersect map(`*`, U, 1/3), list)); # Robert Israel, Aug 31 2020 CROSSREFS Cf. A068791. Sequence in context: A265107 A217631 A046209 * A273348 A198951 A371709 Adjacent sequences: A285882 A285883 A285884 * A285886 A285887 A285888 KEYWORD nonn AUTHOR Enrique Navarrete, Apr 27 2017 STATUS approved

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Last modified May 23 06:14 EDT 2024. Contains 372760 sequences. (Running on oeis4.)