cp's OEIS Frontend

A163248 Sum of the n-th composite number plus the number of composite numbers less than the n-th noncomposite number.

%I A163248 #17 Dec 08 2015 08:57:37
%S A163248 4,6,8,10,12,17,20,24,26,31,38,40,46,51,53,57,63,69,72,79,83,85,91,95,
%T A163248 102,110,114,117,122,124,128,143,147,153,155,165,168,174,180,184,190,
%U A163248 197,200,210,212,216,218,231,243,247
%N A163248 Sum of the n-th composite number plus the number of composite numbers less than the n-th noncomposite number.
%H A163248 Bo Gyu Jeong, <a href="/A163248/b163248.txt">Table of n, a(n) for n = 1..10000</a>
%F A163248 a(n) = A002808(n) + A162177(n) = A008578(n) + A073169(n).
%p A163248 nnc:= 1: nc:= 0; b[nnc]:= 0:b[0]:= 0:
%p A163248 for x from 2 to 1000 do
%p A163248    if isprime(x) then
%p A163248      nnc:= nnc+1; b[nnc]:= b[nnc-1];
%p A163248    else
%p A163248      b[nnc]:= b[nnc]+1;
%p A163248      nc:= nc+1;
%p A163248      c[nc]:= x;
%p A163248    fi
%p A163248 od:
%p A163248 seq(b[n-1]+c[n],n=1..min(nnc,nc)); # _Robert Israel_, Jan 09 2015
%K A163248 nonn,easy,less
%O A163248 1,1
%A A163248 _Jaroslav Krizek_, Jul 23 2009
%E A163248 Corrected for Aug 2009 change of offset in A158611 and A008578 by _Jaroslav Krizek_, Jan 27 2010