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A109403
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Examine the sequence of all (even or odd) semiprimes, A001358, and record the averages of any pair of successive terms of the same parity.
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1
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5, 12, 18, 50, 53, 56, 60, 67, 89, 92, 113, 120, 126, 131, 144, 160, 173, 184, 186, 204, 211, 216, 220, 236, 242, 248, 251, 266, 276, 288, 290, 293, 300, 304, 307, 320, 322, 328, 337, 340, 368, 374, 379, 384, 392
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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LINKS
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EXAMPLE
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5 is OK because sp(1)=4, sp(2)=6 and (4+6)/2=5; 12 is OK because sp(4)=10, sp(5)=14 and (10+14)/2=12; sp(n)=n-th semiprime.
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MAPLE
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A001358 := proc(n) option remember; local a; if n = 1 then 4; else for a from procname(n-1)+1 do if numtheory[bigomega](a) = 2 then return a; end if; end do: end if; end proc:
# To produce a b-file
M:=50000; c:=0;
for n from 1 to M do
lprint(c, m);
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MATHEMATICA
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Select[Mean/@Partition[Select[Range[400], PrimeOmega[#]==2&], 2, 1], IntegerQ] (* Harvey P. Dale, Aug 27 2020 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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Definition corrected by N. J. A. Sloane, Aug 26 2020. The original definition appeared to be based on A100484, but that was incorrect. Thanks to Harvey P. Dale for pointing out that something was wrong.
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STATUS
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approved
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