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

4, 6, 8, 10, 12, 17, 20, 24, 26, 31, 38, 40, 46, 51, 53, 57, 63, 69, 72, 79, 83, 85, 91, 95, 102, 110, 114, 117, 122, 124, 128, 143, 147, 153, 155, 165, 168, 174, 180, 184, 190, 197, 200, 210, 212, 216, 218, 231, 243, 247

Offset: 1

Author

Jaroslav Krizek, Jul 23 2009

Keywords

• nonn
• easy
• less

Links

• Bo Gyu Jeong, Table of n, a(n) for n = 1..10000

Programs

Maple

nnc:= 1: nc:= 0; b[nnc]:= 0:b[0]:= 0:
for x from 2 to 1000 do
   if isprime(x) then
     nnc:= nnc+1; b[nnc]:= b[nnc-1];
   else
     b[nnc]:= b[nnc]+1;
     nc:= nc+1;
     c[nc]:= x;
   fi
od:
seq(b[n-1]+c[n],n=1..min(nnc,nc)); # Robert Israel, Jan 09 2015

Formula

a(n) = A002808(n) + A162177(n) = A008578(n) + A073169(n).

Extensions

Corrected for Aug 2009 change of offset in A158611 and A008578 by Jaroslav Krizek, Jan 27 2010