1 ! Copyright (c) 2008 Eric Mertens
2 ! See http://factorcode.org/license.txt for BSD license.
3 USING: kernel math math.functions sequences sequences.lib ;
9 : sum-1toN ( n -- sum )
13 [ dup 0 > ] [ 7 /mod ] [ ] unfold nip ;
15 : (use-digit) ( prev x index -- next )
16 [ [ 1+ * ] [ sum-1toN 7 sum-1toN ] bi ] dip ^ * + ;
20 : (euler148) ( x -- y )
21 >base7 0 [ (use-digit) ] reduce-index ;