The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A181623 Sequence starting with 1 such that the sum of any two distinct elements has four distinct prime factors. 0
 1, 209, 1121, 2989, 11381, 34889, 47701, 62453, 188785, 878185, 1761737, 3931385, 5630905, 7990481, 32892077, 204570037, 253223785, 1353794333, 2877954833 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Choose the first number not leading to a contradiction. LINKS EXAMPLE Each of the three pairwise sums of the subset {1, 209, 1121} is the product of four distinct prime factors: {2*3*5*7, 2*3*11*17, 2*3*5*137}. MAPLE with(numtheory):nn:=100000:T:=array(1..nn): U:=array(1..nn): for p from 1 to nn do: T[p]:=p:U[p]:=1:od:for u from 1 to 30 do: k:=1+u:for n from u+1 to nn do:s:=T[n]+T[u]:s1:=nops(factorset(s)):s2:=bigomega(s):if s1=4 and s2=4 then U[k]:=T[n]:k:=k+1:else fi:od:for i from 1 to nn do:T[i]:=U[i]:od:od:for j from 1 to 30 do:printf(`%d, `, T[j]):od: CROSSREFS Cf. A180514, A180565, A180615, A181620, A181622. Sequence in context: A203048 A203041 A293981 * A104874 A157441 A304063 Adjacent sequences: A181620 A181621 A181622 * A181624 A181625 A181626 KEYWORD nonn AUTHOR Michel Lagneau, Jan 31 2011 EXTENSIONS a(9)-a(19) from Donovan Johnson, Feb 14 2011 STATUS approved

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

Last modified March 26 06:47 EDT 2023. Contains 361529 sequences. (Running on oeis4.)