OFFSET
1,1
COMMENTS
Sequence contains numbers of the forms 5 + 60*k, 10 + 60*k, 20 + 60*k, 25 + 60*k, 35 + 60*k, 40 + 60*k, 50 + 60*k, 55 + 60*k, where k>=0.
Numbers that are congruent to {5, 10, 20, 25} mod 30. - Amiram Eldar, Jan 01 2022
LINKS
FORMULA
a(n) = 15*(n-1)-a(n-1), with a(1)=5. - Vincenzo Librandi, Aug 08 2010
a(1)=5, a(2)=10, a(3)=20, a(n)=a(n-1)+a(n-2)-a(n-3). - Harvey P. Dale, May 15 2011
a(n) = -(5/4)*(3+(-1)^n-6*n). - Harvey P. Dale, May 15 2011
G.f.: 5*x*(x^2+x+1) / ((x-1)^2*(x+1)). - Colin Barker, Jun 16 2013
Sum_{n>=1} (-1)^(n+1)/a(n) = Pi/(15*sqrt(3)) = A248897 / 10. - Amiram Eldar, Jan 01 2022
MATHEMATICA
Flatten[Position[Fibonacci[Range[400]], _?(Last[IntegerDigits[#]]==5&)]] (* or *) LinearRecurrence[{1, 1, -1}, {5, 10, 20}, 60] (* or *) Table[-(5/4) (3+(-1)^n-6 n), {n, 60}] (* Harvey P. Dale, May 15 2011 *)
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Benoit Cloitre, Aug 07 2002
EXTENSIONS
Edited by M. F. Hasler, Oct 08 2014
STATUS
approved