cp's OEIS Frontend

A356123 Least Lucas number with n Lucas divisors.

%I A356123 #18 Aug 24 2022 12:09:06
%S A356123 1,2,4,18,1364,1860498,2537720636,6440026026380244498,
%T A356123 8784200221406821330636,77162173529763648886126034136172445632164498,
%U A356123 4365101043708483494615466932242949707161871659736799144058331102381689400753867700636
%N A356123 Least Lucas number with n Lucas divisors.
%H A356123 Daniel Suteu, <a href="/A356123/b356123.txt">Table of n, a(n) for n = 1..21</a>
%F A356123 a(n) = A000032(A356666(n)). - _Daniel Suteu_, Aug 24 2022
%o A356123 (PARI) L(n)=fibonacci(n+1)+fibonacci(n-1); \\ A000032
%o A356123 isld(n) = { my(u1=1, u2=3, old_u1); if(n<=2, sign(n), while(n>u2, old_u1=u1; u1=u2; u2=old_u1+u2); (u2==n)); }; \\ A102460
%o A356123 nbld(n) = sumdiv(n, d, isld(d)); \\ A304092
%o A356123 a(n) = my(k=0); while(nbld(L(k)) != n, k++); L(k);
%o A356123 (PARI)
%o A356123 countLd(n) = my(c=0,x=2,y=1); while(x <= n, if(n%x == 0, c++); [x,y]=[y,x+y]); c;
%o A356123 a(n) = if(n==1, return(1)); my(x=2,y=1); while(1, if(countLd(x) == n, return(x)); [x,y]=[y,x+y]); \\ _Daniel Suteu_, Aug 24 2022
%Y A356123 Cf. A000032, A102460, A304092, A356062, A356122, A356666.
%Y A356123 Cf. A076985 (similar for Fibonacci numbers).
%K A356123 nonn
%O A356123 1,2
%A A356123 _Michel Marcus_, Jul 27 2022
%E A356123 a(11) from _Daniel Suteu_, Aug 06 2022