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A345407
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a(n) is the first semiprime that starts a sequence of n distinct semiprimes under the map A001414.
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0
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4, 9, 14, 33, 62, 177, 886, 2649, 5294, 68653, 496966, 1490889, 16896262
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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a(1) = 4 which is a semiprime (note 2*2 = 2+2, which is why the word "distinct" is in the Name).
a(3) = 14 = 2*7 -> 9 (semiprime) = 3*3 -> 3+3 = 6 (semiprime) = 2*3 -> 2+3 = 5 (not semiprime).
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MAPLE
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f:= proc(n) local L, a, b; option remember;
L:= ifactors(n)[2];
if nops(L) = 1 and L[1][2] = 2 then
1 + procname(2*L[1][1])
elif nops(L) = 2 and L[1][2]+L[2][2]=2 then
1 + procname(L[1][1]+L[2][1])
else 0
fi
end proc:
f(4):= 1:
V:= map(f, [$1..10^6]):
W:= Vector(11):
for nn from 1 to 10^6 do
if V[nn] > 0 and W[V[nn]] = 0 then W[V[nn]]:= nn fi
od:
convert(W, list);
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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