A061471 First (leftmost) digit - second digit + third digit - fourth digit .... = 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

Author

Amarnath Murthy, May 05 2001

Keywords

• nonn
• base
• easy

Comments

a(n) == 9*(-1)^d (mod 11) if a(n) has d digits. - Robert Israel, Aug 05 2020

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A008593, A060978-A060980, A060982, A061470-A061479, A061870-A061882.

Programs

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 *)

Extensions

More terms from Robert G. Wilson v, May 10 2001 and from Larry Reeves (larryr(AT)acm.org), May 14 2001