cp's OEIS Frontend

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.

A167346 Totally multiplicative sequence with a(p) = (p-1)*(p+2) = p^2+p-2 for prime p.

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%I A167346 #17 Nov 05 2022 08:17:56
%S A167346 1,4,10,16,28,40,54,64,100,112,130,160,180,216,280,256,304,400,378,
%T A167346 448,540,520,550,640,784,720,1000,864,868,1120,990,1024,1300,1216,
%U A167346 1512,1600,1404,1512,1800,1792,1720,2160,1890,2080,2800,2200,2254,2560,2916,3136
%N A167346 Totally multiplicative sequence with a(p) = (p-1)*(p+2) = p^2+p-2 for prime p.
%H A167346 G. C. Greubel, <a href="/A167346/b167346.txt">Table of n, a(n) for n = 1..1000</a>
%F A167346 Multiplicative with a(p^e) = ((p-1)*(p+2))^e. If n = Product p(k)^e(k) then a(n) = Product ((p(k)-1)*(p(k)+2))^e(k).
%F A167346 a(n) = A003958(n) * A166590(n).
%F A167346 Sum_{k>=1} 1/a(k) = Product_{primes p} (1 + 1/(p^2 + p - 3)) = 1.611922780552146990915794949248803526278171368254928942581015265238806543... - _Vaclav Kotesovec_, Sep 20 2020
%F A167346 Sum_{k=1..n} a(k) ~ c * n^3, where c =  2/(Pi^2 * Product_{p prime} (1 - 2/p^2 + 1/p^3 + 2/p^4)) = 0.3809790887... . - _Amiram Eldar_, Nov 05 2022
%t A167346 a[1] = 1; a[n_] := (fi = FactorInteger[n]; Times @@ ((fi[[All, 1]] - 1)^fi[[All, 2]])); b[1] = 1; b[n_] := (fi = FactorInteger[n]; Times @@ ((fi[[All, 1]] + 2)^fi[[All, 2]])); Table[a[n]*b[n], {n, 1, 100}] (* _G. C. Greubel_, Jun 10 2016 *)
%t A167346 f[p_, e_] := ((p - 1)*(p + 2))^e; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* _Amiram Eldar_, Nov 05 2022 *)
%o A167346 (PARI) a(n) = {my(f = factor(n)); prod(i = 1, #f~, ((f[i,1]-1)*(f[i,1]+2))^f[i,2]); } \\ _Amiram Eldar_, Nov 05 2022
%Y A167346 Cf. A003958, A166590.
%K A167346 nonn,mult
%O A167346 1,2
%A A167346 _Jaroslav Krizek_, Nov 01 2009