A. V. Aho and N. J. A. Sloane, <a href="httphttps://neilsloanewww.fq.math.comca/Scanned/doc11-4/doublyaho-a.htmlpdf">Some doubly exponential sequences</a>, Fib. QuartFibonacci Quarterly, Vol., 11 , No. 4 (1973), pp. 429-437, <a href="http://neilsloane.com/doc/doubly.html">alternative