OFFSET
1,1
LINKS
FORMULA
Define F(x) = x(x+1)/2. Write 2n+1 = 2^i*m + 2^(i-1) + 1, then a(n) = (1/2)F^(i-1)(2n+1). E.g. n=4, 2n+1 = 9 = 2^4*0 + 2^3 + 1, so i=4, m=0 and F(F(F(9))) = F(F(45)) = F(1035) = 536130, a(4) = 536130/2 = 268065.
MATHEMATICA
a[n_]:=Module[{b=(2n+1)/2}, While[!IntegerQ[b], b*=Ceiling[b]]; b]; Array[a, 31] (* Stefano Spezia, Jun 26 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Apr 13 2003
EXTENSIONS
a(30)-a(31) from Stefano Spezia, Jun 26 2024
STATUS
approved