login

Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.

a(n) = sigma(n) + sigma(n+1) + sigma(n+2) - sigma(n+3), where sigma is the sum of divisors.
3

%I #15 Nov 02 2021 22:25:14

%S 1,8,5,17,11,22,18,34,15,44,30,42,31,61,34,68,35,69,58,86,32,89,73,93,

%T 57,108,54,126,71,119,89,117,59,155,117,133,64,164,92,184,98,146,134,

%U 186,74,187,136,202,124,209,104,200,126,232,182,230,62,256,194,222,135,243,171,287,170

%N a(n) = sigma(n) + sigma(n+1) + sigma(n+2) - sigma(n+3), where sigma is the sum of divisors.

%H Michel Marcus, <a href="/A348688/b348688.txt">Table of n, a(n) for n = 1..11000</a>

%t Array[#+#2+#3-#4&@@DivisorSigma[1,{#,#+1,#+2,#+3}]&,100] (* _Giorgos Kalogeropoulos_, Oct 29 2021 *)

%o (PARI) a(n) = sigma(n) + sigma(n+1) + sigma(n+2) - sigma(n+3);

%Y Cf. A000203, A348335, A348689, A348698 (a(n) <= 0).

%K sign

%O 1,2

%A _Michel Marcus_, Oct 29 2021