A075832 Let u(1) = u(2) = u(3) = u(4) = 1, u(n+4)*(n+4) = u(n+3)*(n+3)+u(n+2)*(n+2)+u(n+1)*(n+1)+u(n)*n; sequence gives values of n such that u(n) is an integer.

1, 2, 3, 4, 5, 67, 150, 154, 387, 547, 813, 1034, 1710, 4994, 13582, 700427, 1598953, 2960411

Offset

1,2

Comments

No more terms up to n=15*10^6. - Lambert Klasen (Lambert.Klasen(AT)gmx.net) and Robert G. Wilson v, Aug 05 2005

Links

Table of n, a(n) for n=1..18.

Mathematica

a = {0, 1, 1, 1, 1}; Do[a = Rest[ Join[a, {((n - 4)a[[2]] + (n - 3)a[[3]] + (n - 2)a[[4]] + (n - 1)a[[5]])/n}]]; If[ IntegerQ[ Last[ a]], Print[n]], {n, 5, 2*10^6}] (* Robert G. Wilson v *)

Prog

(PARI) v = [1, 1, 1, 1]; for(k=0, 15, s=k*10^6+1; e=(k+1)*10^6; if(s==1, s=5); print(s, " - ", e, ":"); for(n=s, e, v[(n-1)%4+1]=((n-4)*v[(n-1)%4+1]+(n-3)*v[(n)%4+1]+(n-2)*v[(n+1)%4+1]+(n-1)*v[(n+2)%4+1])/n; if(denominator(v[(n-1)%4+1])==1, print1(n, ", "))); print()) \\ (Klasen)

Crossrefs

Cf. A075770.

Sequence in context: A004856 A325653 A037327 * A037434 A033170 A374431

Adjacent sequences: A075829 A075830 A075831 * A075833 A075834 A075835

Keyword

nonn

Author

Benoit Cloitre, Oct 14 2002

Extensions

Corrected and extended by Lambert Klasen (Lambert.Klasen(AT)gmx.net) and Robert G. Wilson v, Aug 05 2005

Status

approved