This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A163296 #14 Jul 21 2025 10:32:46
%S A163296 0,1,2,3,4,5,5,6,7,8,8,9,10,11,11,12,13,13,14,14,15,16,17,17,18,18,19,
%T A163296 20,20,21,22,23,23,24,25,25,26,26,27,28,28,29,29,30,31,32,32,33,33,34,
%U A163296 35,35,36,37,38,38,39,39,40,41,41,42,43,43,44,44,45,46,46,47,47,48,48,49,50,50,51,52,53,53
%N A163296 Absolute value of the Sum_{x=0..A141468(n)} x*(-1)^x.
%H A163296 G. C. Greubel, <a href="/A163296/b163296.txt">Table of n, a(n) for n = 1..1000</a>
%F A163296 a(n) = |A130472(A141468(n))|. - _R. J. Mathar_, Jul 26 2009
%e A163296 a(1)=abs(0*(-1)^0)=1, a(2)=abs(0*(-1)^0+1*(-1)^1)=1-1=0, a(3)=abs(1-1+2-3+4)=3, a(4)=abs(1-1+2-3+4-5+6)=4, a(5)=abs(1-1+2-3+4-5+6-7+8)=5, a(6)=abs(1-1+2-3+4-5+6-7+8-9)=abs(-4)=4.
%p A163296 A130472 := proc(n) (-1)^n*floor((n+1)/2) ; end: A141468 := proc(n) option remember; local a; if n = 1 then 0 ; else for a from procname(n-1)+1 do if not isprime(a) then RETURN(a) ; fi; od: fi; end: A163296 := proc(n) abs(A130472( A141468(n))) ; end: seq(A163296(n),n=1..100) ; # _R. J. Mathar_, Jul 26 2009
%t A163296 nonPrime[n_Integer] := FixedPoint[n + PrimePi@# &, n + PrimePi@n]; Table[Abs[Sum[k*(-1)^k, {k, 0, nonPrime[n]}]], {n,0,50}] (* _G. C. Greubel_, Dec 18 2016 *)
%Y A163296 Cf. A141468.
%K A163296 nonn,less
%O A163296 1,3
%A A163296 _Juri-Stepan Gerasimov_, Jul 24 2009
%E A163296 Corrected by _R. J. Mathar_, Jul 26 2009