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%I #14 Mar 01 2023 15:13:35
%S 2,20,31,42,53,64,75,86,97,101,112,123,134,145,156,167,178,189,200,
%T 211,222,233,244,255,266,277,288,299,310,321,332,343,354,365,376,387,
%U 398,420,431,442,453,464,475,486,497,530,541,552,563,574,585,596,640,651
%N First (leftmost) digit - second digit + third digit - fourth digit .... = 2.
%C a(n) == 9*(-1)^d (mod 11) if a(n) has d digits. - _Robert Israel_, Aug 05 2020
%H Robert Israel, <a href="/A061471/b061471.txt">Table of n, a(n) for n = 1..10000</a>
%p filter:= proc(n) local d,L,j;
%p L:= convert(n,base,10);
%p d:= nops(L);
%p add(L[j]*(-1)^(d-j),j=1..d)=2
%p end proc:
%p select(filter, [$1..1000]); # _Robert Israel_, Aug 05 2020
%t okQ[n_] := With[{id = IntegerDigits[n]}, id.Array[2 Mod[#, 2] - 1&, Length[id]] == 2]; Select[Range[1000], okQ] (* _Jean-François Alcover_, Nov 17 2016 *)
%t Select[Range[700],Total[Times@@@Partition[Riffle[IntegerDigits[#],{1,-1},{2,-1,2}],2]] == 2&] (* _Harvey P. Dale_, Mar 01 2023 *)
%Y Cf. A008593, A060978-A060980, A060982, A061470-A061479, A061870-A061882.
%K nonn,base,easy
%O 1,1
%A _Amarnath Murthy_, May 05 2001
%E More terms from _Robert G. Wilson v_, May 10 2001 and from Larry Reeves (larryr(AT)acm.org), May 14 2001
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