A181622 Sequence starting with 1 such that the sum of any two distinct terms has three distinct prime factors.

1, 29, 41, 281, 401, 1089, 1585, 2289, 4629, 27293, 74873, 965813, 2536781, 4479197, 36730306, 150318056, 4527046433

Offset: 1

Author

Michel Lagneau, Jan 31 2011

Keywords

• nonn

Comments

Choose the first number not leading to a contradiction.

Examples

			Each of the three pairwise sums of the subset {29, 41, 281} is the product of three distinct prime factors: {2*5*7, 2*5*31, 2*7*23}.
		

Crossrefs

Cf. A180514, A180565, A180615, A181620.

Programs

Maple

with(numtheory):nn:=200000: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 20 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=3 and s2=3 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:

Extensions

a(12)-a(17) from Donovan Johnson, Feb 14 2011