Data commit

Task/Van-Eck-sequence/Tcl/van-eck-sequence.tcl

@@ -0,0 +1,24 @@
+## Mathematically, the first term has index "0", not "1".  We do that, also.
+
+set ::vE 0
+
+proc vanEck {n} {
+    global vE vEocc
+    while {$n >= [set k [expr {[llength $vE] - 1}]]} {
+        set kv [lindex $vE $k]
+        ## value $kv @ $k is not yet stuffed into vEocc()
+        lappend vE [expr {[info exists vEocc($kv)] ? $k - $vEocc($kv) : 0}]
+        set vEocc($kv) $k
+    }
+    return [lindex $vE $n]
+}
+
+proc show {func from to} {
+    for {set n $from} {$n <= $to} {incr n} {
+        append r " " [$func $n]
+    }
+    puts "${func}($from..$to) =$r"
+}
+
+show vanEck 0 9
+show vanEck 990 999