A068334 - OEIS

%I #19 Apr 14 2021 09:23:55

%S 1,2,3,4,9,10,61,62,497,1492,26857,26858,6445921,6445922,786402485,

%T 21232867096,10531502079617,10531502079618,314049392014208761,

%U 314049392014208762,33736441887734362049089,6173768865455388254983288

%N a(1) = 1; a(n+1) = 1 + Product_{k|n} a(k), product is over the positive divisors, k, of n.

%H Seiichi Manyama, <a href="/A068334/b068334.txt">Table of n, a(n) for n = 1..66</a>

%e a(7) = 1 + a(1)*a(2)*a(3)*a(6) = 1 + 1*2*3*10 = 61.

%t Nest[Append[#1, 1 + Times @@ #1[[Divisors[#2] ]] ] & @@ {#, Length[#]} &, {1}, 21] (* _Michael De Vlieger_, Apr 13 2021 *)

%o (PARI) lista(nn) = {my(va = vector(nn)); va[1] = 1; for (n=2, nn, my(d=divisors(n-1)); va[n] = 1 + prod(k=1, #d, va[d[k]]);); va;} \\ _Michel Marcus_, Apr 13 2021

%Y Cf. A068336, A343390.

%K nonn

%O 1,2

%A _Leroy Quet_, Feb 27 2002