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 A281006 #22 Sep 25 2018 20:51:04 %S A281006 1,3,2,5,2,8,2,9,5,10,2,18,2,12,10,17,2,23,2,24,12,16,2,38,7,18,14,30, %T A281006 2,44,2,33,16,22,14,57,2,24,18,52,2,56,2,42,34,28,2,78,9,45,22,48,2, %U A281006 68,18,66,24,34,2,110,2,36,42,65,20,80,2,60,28,76,2,125,2,42,50,66,20,92,2,108,41,46,2,142,24,48,34,94,2 %N A281006 a(n) = A000203(n) - A052928(n-1). %C A281006 a(n) = 2 iff n is an odd prime (A065091). %C A281006 Has a symmetric representation as a narrow pyramid with holes, in the same way as A249351. %H A281006 Antti Karttunen, <a href="/A281006/b281006.txt">Table of n, a(n) for n = 1..65537</a> %H A281006 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a> %F A281006 a(n) = sigma(n) - 2*floor((n - 1)/2) = A000203(n) - 2*A004526(n-1). %F A281006 a(n) = A048050(n) + A176059(n), n >= 2. %e A281006 A000203 A052928 a(n) %e A281006 . 1 - 0 = 1 %e A281006 . 3 - 0 = 3 %e A281006 . 4 - 2 = 2 %e A281006 . 7 - 2 = 5 %e A281006 . 6 - 4 = 2 %e A281006 . 12 - 4 = 8 %e A281006 ... %o A281006 (PARI) A281006(n) = (sigma(n) - 2*((n-1)>>1)); \\ _Antti Karttunen_, Sep 25 2018 %Y A281006 Cf. A000203, A004526, A048050, A052928, A065091, A176059, A196020, A235791, A236104, A237048, A237270, A237271, A237591, A237593, A245092, A249351, A262626, A279387, A281010. %K A281006 nonn %O A281006 1,2 %A A281006 _Omar E. Pol_, Jan 23 2017