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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. 0
1, 2, 3, 4, 5, 67, 150, 154, 387, 547, 813, 1034, 1710, 4994, 13582, 700427, 1598953, 2960411 (list; graph; refs; listen; history; text; internal format)
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: A069881 A004856 A037327 * A037434 A033170 A097931

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

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Last modified May 19 06:53 EDT 2019. Contains 323386 sequences. (Running on oeis4.)