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a(n) = A000203(n) - A052928(n-1).
1

%I #22 Sep 25 2018 20:51:04

%S 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 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 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 a(n) = A000203(n) - A052928(n-1).

%C a(n) = 2 iff n is an odd prime (A065091).

%C Has a symmetric representation as a narrow pyramid with holes, in the same way as A249351.

%H Antti Karttunen, <a href="/A281006/b281006.txt">Table of n, a(n) for n = 1..65537</a>

%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>

%F a(n) = sigma(n) - 2*floor((n - 1)/2) = A000203(n) - 2*A004526(n-1).

%F a(n) = A048050(n) + A176059(n), n >= 2.

%e A000203 A052928 a(n)

%e . 1 - 0 = 1

%e . 3 - 0 = 3

%e . 4 - 2 = 2

%e . 7 - 2 = 5

%e . 6 - 4 = 2

%e . 12 - 4 = 8

%e ...

%o (PARI) A281006(n) = (sigma(n) - 2*((n-1)>>1)); \\ _Antti Karttunen_, Sep 25 2018

%Y Cf. A000203, A004526, A048050, A052928, A065091, A176059, A196020, A235791, A236104, A237048, A237270, A237271, A237591, A237593, A245092, A249351, A262626, A279387, A281010.

%K nonn

%O 1,2

%A _Omar E. Pol_, Jan 23 2017