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A100915
Numbers n such that n plus n-th semiprime is semiprime.
5
4, 6, 9, 12, 16, 18, 19, 20, 24, 29, 31, 34, 35, 39, 40, 44, 46, 49, 51, 54, 55, 72, 73, 76, 79, 80, 81, 84, 87, 91, 93, 94, 96, 98, 110, 113, 116, 120, 128, 130, 136, 137, 148, 150, 154, 159, 165, 168, 170, 172, 175, 188, 190, 191, 199, 200, 206, 215, 217, 220, 230
OFFSET
1,1
COMMENTS
This is the semiprime analog of A064402.
LINKS
Eric Weisstein, World of Mathematics, Semiprime.
FORMULA
a(n) = A100466(n) - A100916(n) = A100466(n) - A001358(A100915(n)).
EXAMPLE
a(3) = 9 because 9 + semiprime(9) = 9 + 25 = 34 is semiprime.
MATHEMATICA
With[{c=Select[Range[1000], PrimeOmega[#]==2&]}, Transpose[Select[Thread[ {c, Range[ Length[c]]}], PrimeOmega[Total[#]]==2&]][[2]]] (* Harvey P. Dale, Oct 25 2011 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Ray Chandler, Nov 26 2004
STATUS
approved