A181623 Sequence starting with 1 such that the sum of any two distinct elements has four distinct prime factors.

1, 209, 1121, 2989, 11381, 34889, 47701, 62453, 188785, 878185, 1761737, 3931385, 5630905, 7990481, 32892077, 204570037, 253223785, 1353794333, 2877954833

Offset

1,2

Comments

Choose the first number not leading to a contradiction.

Links

Table of n, a(n) for n=1..19.

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