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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

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 August 1 05:43 EDT 2014. Contains 245104 sequences.