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A181623
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Sequence starting with 1 such that the sum of any two distinct elements has four distinct prime factors.
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0
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1, 209, 1121, 2989, 11381, 34889, 47701, 62453, 188785, 878185, 1761737, 3931385, 5630905, 7990481, 32892077, 204570037, 253223785, 1353794333, 2877954833
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OFFSET
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1,2
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COMMENTS
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Choose the first number not leading to a contradiction.
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LINKS
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Table of n, a(n) for n=1..19.
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EXAMPLE
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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}.
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MAPLE
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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:
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CROSSREFS
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Cf. A180514, A180565, A180615, A181620, A181622.
Sequence in context: A203048 A203041 A293981 * A104874 A157441 A304063
Adjacent sequences: A181620 A181621 A181622 * A181624 A181625 A181626
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KEYWORD
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nonn
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AUTHOR
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Michel Lagneau, Jan 31 2011
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EXTENSIONS
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a(9)-a(19) from Donovan Johnson, Feb 14 2011
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STATUS
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approved
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