Leonardo number
The Leonardo numbers are a sequence of numbers given by the recurrence: L ( n ) = { 1 if n = 0 1 if n = 1 L ( n − 1 ) + L ( n − 2 ) + 1 if n > 1 {\displaystyle L(n)={\begin{cases}1&{\mbox{if }}n=0\\1&{\mbox{if }}n=1\\L(n-1)+L(n-2)+1&{\mbox{if }}n>1\\\end{cases}}} Edsger W. Dijkstra used them as an integral part of his smoothsort algorithm, and also analyzed them in some detail. A Leonardo prime is a Leonardo number that is also prime.