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 A206011 The n-th semiprime minus its sum of digits. 1
 0, 0, 0, 9, 9, 9, 18, 18, 18, 18, 27, 27, 27, 27, 27, 36, 36, 45, 45, 45, 45, 54, 54, 54, 63, 63, 72, 72, 72, 72, 81, 81, 81, 81, 99, 108, 108, 108, 108, 117, 117, 117, 117, 126, 126, 135, 135, 135, 135, 135, 144, 144, 144, 153, 153, 153, 162, 162, 171, 171 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS This is to semiprimes A001358 as A068395 is to primes A000040. As with A068395, this is always a multiple of 9, hence cannot be prime. But, as happens first for a(4), a(n) can be semiprime. LINKS Table of n, a(n) for n=1..60. FORMULA a(n) = A001358(n) - A007953(A001358(n)). EXAMPLE a(4) = 10 - 1 = 9. a(5) = 14 - 5 = 9. MAPLE read("transforms") : A206011 := proc(n) s := A001358(n) ; s -digsum(s) ; end proc: # R. J. Mathar, Sep 14 2012 MATHEMATICA #-Total[IntegerDigits[#]]&/@Select[Range[200], PrimeOmega[#]==2&] (* Harvey P. Dale, Nov 24 2022 *) CROSSREFS Cf. A000040, A001358, A007953, A068395. Sequence in context: A144586 A141557 A072563 * A192984 A069602 A160761 Adjacent sequences: A206008 A206009 A206010 * A206012 A206013 A206014 KEYWORD nonn,easy,base AUTHOR Jonathan Vos Post, Feb 02 2012 STATUS approved

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Last modified December 9 16:37 EST 2023. Contains 367693 sequences. (Running on oeis4.)