OFFSET
1,3
COMMENTS
No other terms < 10^6. - T. D. Noe, Aug 25 2012
This sequence maps to the Ramanujan-Nagell squares (8*(k*(k+1)/2)+1) and is therefore complete. - Raphie Frank, Aug 26 2012
All terms in this sequence follow form floor[2^((2*x - 1)/2)]; x = {0, 1, 2, 3, 7}. - Raphie Frank, Mar 03 2013
LINKS
Eric W. Weisstein, MathWorld: Ramanujan's Square Equation
FORMULA
a(n) = -1 + ceiling[sqrt(2^(A060728(n) - 2) - 1)]. - Raphie Frank, Mar 31 2013
a(n) = (|(((1+i*sqrt(7))/2)^(A060728(n) - 2) + ((1-i*sqrt(7))/2)^(A060728(n) - 2))| - 1)/2. - Raphie Frank, Dec 25 2013
MATHEMATICA
Select[Range[0, 1000], IntegerQ[Log[2, 1 + #(#+1)/2]]&] (* T. D. Noe, Aug 25 2012 *)
PROG
(PARI) for(n=0, 100, if(ispolygonal(2^n-1, 3), print1(sqrtint(2*2^n-2)", "))) \\ Charles R Greathouse IV, Mar 04 2013
CROSSREFS
KEYWORD
nonn,fini,full
AUTHOR
V. Raman, Aug 23 2012
STATUS
approved