A356123 Least Lucas number with n Lucas divisors.

1, 2, 4, 18, 1364, 1860498, 2537720636, 6440026026380244498, 8784200221406821330636, 77162173529763648886126034136172445632164498, 4365101043708483494615466932242949707161871659736799144058331102381689400753867700636

Offset: 1

Author

Michel Marcus, Jul 27 2022

Keywords

• nonn

Links

• Daniel Suteu, Table of n, a(n) for n = 1..21

Crossrefs

Cf. A000032, A102460, A304092, A356062, A356122, A356666.

Cf. A076985 (similar for Fibonacci numbers).

Programs

PARI

L(n)=fibonacci(n+1)+fibonacci(n-1); \\ A000032
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
nbld(n) = sumdiv(n, d, isld(d)); \\ A304092
a(n) = my(k=0); while(nbld(L(k)) != n, k++); L(k);

PARI

countLd(n) = my(c=0,x=2,y=1); while(x <= n, if(n%x == 0, c++); [x,y]=[y,x+y]); c;
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

Formula

a(n) = A000032(A356666(n)). - Daniel Suteu, Aug 24 2022

Extensions

a(11) from Daniel Suteu, Aug 06 2022