A206011 The n-th semiprime minus its sum of digits.

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

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