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A111156 Numbers that look the same when printed upside down. 3

%I

%S 0,8,69,88,96,609,689,808,888,906,986,6009,6699,6889,6969,8008,8698,

%T 8888,8968,9006,9696,9886,9966,60009,60809,66099,66899,68089,68889,

%U 69069,69869,80008,80808,86098,86898,88088,88888,89068,89868,90006,90806,96096,96896,98086,98886,99066,99866,600009

%N Numbers that look the same when printed upside down.

%C Numbers with 1's are excluded.

%C Numbers written with digits 0,6,8,9, with 6 and 9 interchanged when reversed. - _Robert Israel_, Jul 02 2018

%H Robert Israel, <a href="/A111156/b111156.txt">Table of n, a(n) for n = 1..10000</a>

%p f:= proc(n) local L,Lp,nl;

%p L:= subs(1=6,2=8,3=9,convert(n,base,4));

%p nl:= nops(L);

%p Lp:= subs([6=9,9=6],L);

%p add(Lp[-i]*10^(i-1),i=1..nl)+add(L[i]*10^(nl+i-1),i=1..nl);

%p end proc:

%p g:= proc(n) local L,Lp,nl;

%p L:= subs(1=6,2=8,3=9,convert(n,base,4));

%p nl:= nops(L);

%p Lp:= subs([6=9,9=6],L);

%p seq(add(Lp[-i]*10^(i-1),i=1..nl)+x*10^nl+add(L[i]*10^(nl+i),i=1..nl),x=[0,8]);

%p end proc:

%p 0,8,seq(op([seq(f(n),n=4^i..4^(i+1)-1),seq(g(n),n=4^i..4^(i+1)-1)]),i=0..2); # _Robert Israel_, Jul 02 2018

%o {-Haskell-} main=print$"0":concat[concat[[reverse(reverse(map f x)++z++x)|x<-y]|z<-["","0"]]|y<-s(iterate i"6")];f '0'='0';f '6'='9';f '8'='8';f '9'='6';i('0':x)='6':x;i('6':x)='8':x;i('8':x)='9':x;i('9':x)='0':i x;i""="6";s(x:y@(z:_))=let w:v=s y in if length x==length z then(x:w):v else[x]:w:v

%Y Cf. strobogrammatic numbers A000787. If 8's are excluded we get A111065.

%K base,easy,nonn

%O 1,2

%A Paul Stoeber (pstoeber(AT)uni-potsdam.de), Oct 09 2005

%E Corrected by _Robert Israel_, Jul 02 2018

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Last modified February 21 23:41 EST 2020. Contains 332113 sequences. (Running on oeis4.)