OFFSET
1,2
COMMENTS
Numbers congruent to {1, 26, 129, 224} mod 225.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Colin Barker)
Index entries for linear recurrences with constant coefficients, signature (1,0,0,1,-1).
FORMULA
G.f.: x*(1+25*x+173*x^2+25*x^3+x^4) / ( (1+x)*(1+x^2)*(x-1)^2 ). - R. J. Mathar, Oct 25 2011
a(1)=1, a(2)=26, a(3)=199, a(4)=224, a(5)=226, a(n) = a(n-1)+a(n-4)-a(n-5). - Harvey P. Dale, Nov 11 2011
a(n) = (-225 - 125*(-1)^n + (171-171*i)*(-i)^n + (171+171*i)*i^n + 450*n)/8 where i=sqrt(-1). - Colin Barker, Oct 16 2015
MATHEMATICA
Select[ Range[ 3000 ], PowerMod[ #, 14, 225 ]==1& ]
LinearRecurrence[{1, 0, 0, 1, -1}, {1, 26, 199, 224, 226}, 50] (* Harvey P. Dale, Nov 11 2011 *)
PROG
(PARI) a(n) = (-225 - 125*(-1)^n + (171-171*I)*(-I)^n + (171+171*I)*I^n + 450*n)/8 \\ Colin Barker, Oct 16 2015
(PARI) Vec(x*(1+25*x+173*x^2+25*x^3+x^4)/((1+x)*(1+x^2)*(x-1)^2) + O(x^100)) \\ Colin Barker, Oct 16 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Robert G. Wilson v, Jun 08 2000
STATUS
approved