OFFSET
1,3
COMMENTS
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
Geneviève Paquin, On a generalization of Christoffel words: epichristoffel words, arXiv:0805.4174 [math.CO], 2008-2009.
MAPLE
digrev:= proc(n) local L, i; L:= convert(n, base, 10); add(L[-i]*10^(i-1), i=1..nops(L)) end:
N:=3:
Res:= $0..9:
for d from 2 to N do
if d::even then
m:= d/2;
Res:= Res, seq(n*10^m + digrev(n), n=10^(m-1)..10^m-1);
else
m:= (d-1)/2;
Res:= Res, seq(seq(n*10^(m+1)+y*10^m+digrev(n), y=0..9), n=10^(m-1)..10^m-1);
fi
od:
Palis:= [Res]:
Res:= 0:
for i from 2 to nops(Palis) while Palis[i]^2 <= 10^N do
for j from i to nops(Palis) while Palis[i]*Palis[j] <= 10^N do
Res:= Res, Palis[i]*Palis[j];
od od:sort(convert({Res}, list)); # Robert Israel, Jan 06 2020
MATHEMATICA
pal = Select[ Range[0, 200], # == FromDigits@ Reverse@ IntegerDigits@ # &]; Select[ Union[ Times @@@ Tuples[pal, 2]], # <= 200 &] (* Giovanni Resta, Jun 20 2016 *)
CROSSREFS
KEYWORD
easy,nonn,base
AUTHOR
Jonathan Vos Post, May 28 2008
EXTENSIONS
Data corrected by Giovanni Resta, Jun 20 2016
STATUS
approved