OFFSET
1,2
LINKS
FORMULA
For even-indexed terms, a(n) = 2^n. For odd-indexed terms, a(n) = 7 * 2^(n-3).
G.f.: -x*(x+1)*(3*x+1)/(2*x-1)/(2*x+1). - R. J. Mathar, Nov 14 2007
a(n) = 4*a(n-2) for n > 3; a(1) = 1, a(2) = 4, a(3) = 7. - Klaus Brockhaus, Nov 26 2009
EXAMPLE
a(4) = 16 = sum of row 4 terms of triangle A133599 = (3 + 7 + 5 + 1).
a(4) = 16 = 2^4.
a(7) = 112 = 7 * 2^4 = 7 * 16.
MATHEMATICA
LinearRecurrence[{0, 4}, {1, 4, 7}, 40] (* Harvey P. Dale, Jan 12 2020 *)
PROG
(PARI) {vector(31, n, if(n==1, 1, if(n%2>0, 7*2^(n-3), 2^n)))} /* Klaus Brockhaus, Nov 26 2009 */
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Gary W. Adamson, Sep 18 2007
STATUS
approved