The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A079851 a(1) = 1, a(2) = 2 and a(n) is the smallest number such that all a(i)*a(j) are different. 5
 1, 2, 3, 5, 7, 8, 11, 13, 17, 18, 19, 23, 29, 31, 37, 41, 43, 47, 50, 53, 59, 60, 61, 67, 71, 73, 79, 81, 83, 89, 97, 98, 101, 103, 105, 107, 109, 113, 127, 128, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 242 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Taking a(n) as the smallest number such that a(i)+a(j) are all different gives the Fibonacci sequence (A000045) from third term onwards. Contains all primes. Differs from A066724 in that the latter forbids only the products of distinct terms. - Ivan Neretin, Mar 02 2016 LINKS Ivan Neretin, Table of n, a(n) for n = 1..1000 EXAMPLE After 5, 7 is the next member and not 6 as 6*1 = 2*3. MAPLE A:= 1: F:= {1}: for n from 2 to 100 do   for k from A[n-1]+1 do     Fk:= {k^2, seq(A[i]*k, i=1..n-1)};     if Fk intersect F = {} then        A[n]:= k;        F:= F union Fk;        break     fi   od od: seq(A[i], i=1..100); # Robert Israel, Mar 02 2016 MATHEMATICA nmax = 100; a = 1; F = {1}; For[n = 2, n <= nmax, n++, For[k = a[n-1]+1, True, k++, Fk = Join[{k^2}, Table[a[i]*k, {i, 1, n-1}]] // Union; If[Fk ~Intersection~ F == {}, a[n] = k; F = F ~Union~ Fk; Break[] ]]]; Array[a, nmax] (* Jean-François Alcover, Mar 26 2019, after Robert Israel *) CROSSREFS Cf. A000045, A079850, A079852, compare to A066724. Sequence in context: A331050 A026410 A066720 * A060634 A279457 A171561 Adjacent sequences:  A079848 A079849 A079850 * A079852 A079853 A079854 KEYWORD nonn AUTHOR Amarnath Murthy, Feb 19 2003 EXTENSIONS Corrected and extended by Ray Chandler, Feb 12 2007 Corrected by Ivan Neretin, Mar 02 2016 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 July 14 03:42 EDT 2020. Contains 335716 sequences. (Running on oeis4.)