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A061471
First (leftmost) digit - second digit + third digit - fourth digit .... = 2.
2
2, 20, 31, 42, 53, 64, 75, 86, 97, 101, 112, 123, 134, 145, 156, 167, 178, 189, 200, 211, 222, 233, 244, 255, 266, 277, 288, 299, 310, 321, 332, 343, 354, 365, 376, 387, 398, 420, 431, 442, 453, 464, 475, 486, 497, 530, 541, 552, 563, 574, 585, 596, 640, 651
OFFSET
1,1
COMMENTS
a(n) == 9*(-1)^d (mod 11) if a(n) has d digits. - Robert Israel, Aug 05 2020
LINKS
MAPLE
filter:= proc(n) local d, L, j;
L:= convert(n, base, 10);
d:= nops(L);
add(L[j]*(-1)^(d-j), j=1..d)=2
end proc:
select(filter, [$1..1000]); # Robert Israel, Aug 05 2020
MATHEMATICA
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 *)
Select[Range[700], Total[Times@@@Partition[Riffle[IntegerDigits[#], {1, -1}, {2, -1, 2}], 2]] == 2&] (* Harvey P. Dale, Mar 01 2023 *)
KEYWORD
nonn,base,easy
AUTHOR
Amarnath Murthy, May 05 2001
EXTENSIONS
More terms from Robert G. Wilson v, May 10 2001 and from Larry Reeves (larryr(AT)acm.org), May 14 2001
STATUS
approved