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

1,1

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

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 *)

Crossrefs

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

Sequence in context: A059208 A268742 A261460 * A112271 A201122 A103076

Adjacent sequences: A061468 A061469 A061470 * A061472 A061473 A061474

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