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

1,2

Comments

Choose the first number not leading to a contradiction.

Links

Table of n, a(n) for n=1..17.

Example

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}.

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:

Crossrefs

Cf. A180514, A180565, A180615, A181620.

Sequence in context: A238666 A106019 A084163 * A355599 A086149 A344515

Adjacent sequences: A181619 A181620 A181621 * A181623 A181624 A181625

Keyword

nonn

Author

Michel Lagneau, Jan 31 2011

Extensions

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

Status

approved