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 A368582 #17 Jan 03 2024 05:35:50 %S A368582 1,2,2,4,3,6,4,8,7,9,6,14,7,12,12,16,9,20,10,21,16,18,12,30,16,21,20, %T A368582 28,15,36,16,32,24,27,24,46,19,30,28,45,21,48,22,42,39,36,24,62,29,47, %U A368582 36,49,27,60,36,60,40,45,30,84,31,48,52,64,42,72,34,63 %N A368582 a(n) = floor((sigma(n) + 1) / 2). %F A368582 a(p) = (p + 1) / 2 for all odd prime p. %F A368582 a(n) = n <=> n term of union of A000079 and A000396. (If there are no odd perfect numbers also of A317306). %F A368582 a(n) = floor(A088580(n)/2). - _Omar E. Pol_, Dec 31 2023 %t A368582 Array[Floor[(DivisorSigma[1, #] + 1)/2] &, 120] (* _Michael De Vlieger_, Dec 31 2023 *) %o A368582 (Julia) %o A368582 using Nemo %o A368582 A368582(n::Int) = div(divisor_sigma(n, 1) + 1, 2) %o A368582 println([A368582(n) for n in 1:68]) %o A368582 (PARI) a(n) = (sigma(n)+1)\2; \\ _Michel Marcus_, Jan 03 2024 %Y A368582 Cf. A000203, A000079 (2^n), A000396 (perfect), A088580, A317306, A368207 (Bacher). %K A368582 nonn %O A368582 1,2 %A A368582 _Peter Luschny_, Dec 31 2023