This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A216261 #41 Oct 18 2020 01:49:54
%S A216261 1,7,4,2,0,8,10,18,22,20,28,68,88,108,188,200,208,288,688,888,1088,
%T A216261 1888,2008,2088,2888,6888,8888,10888,18888,20088,20888,28888,68888,
%U A216261 88888,108888,188888,200888,208888,288888,688888,888888,1088888,1888888,2008888,2088888,2888888
%N A216261 Smallest positive number using exactly n segments on a calculator display (when '6' and '7' are represented using 6 resp. 3 segments).
%C A216261 Essentially the same as A038619 and A143617. One could argue that a(3) should rather be -1 (prior to adding "positive" in the definition), which does use 3 segments on typical 7-segment displays, and is smaller than 7. Also, most pocket calculators and the Unicode standard (cf. links) use 4 rather than 3 segments to represent a '7' (as in A074458 and A010371, rather than A063720, A277116 or A006942), in which case a(3) is undefined if negative numbers are not allowed. No digit '9' will ever occur here, whether it would be represented with 6 or only 5 segments. However, digit '6' does occur, as the second smallest digit using 6 segments as does '0', which cannot occur as leading digit. If '6' is represented with 5 segments, any prefix 68 would be replaced with 80. - _M. F. Hasler_ and _Kevin Ryde_, Jun 17 2020
%H A216261 Unicode, <a href="https://www.unicode.org/charts/PDF/U1FB00.pdf">Symbols for Legacy Computing</a>, The Unicode Standard, Version 13.0, 2020.
%H A216261 <a href="/index/Ca#calculatordisplay">Index entries for sequences related to calculator display</a>
%H A216261 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,0,10,-10).
%F A216261 A006942(a(n)) = n and A006942(m) <> n for m < a(n).
%F A216261 a(n+7) = 10*a(n) + 8 for n > 10. This can be deduced from a(n) = min{10*a(n-A006942(r))+r, r=0..9} via strong induction. - _David Radcliffe_, Jan 29 2016
%F A216261 G.f.: (x^2 +6*x^3 -3*x^4 -2*x^5 -2*x^6 +8*x^7 +2*x^8 -2*x^9 -56*x^10 +28*x^11 +28*x^12 +60*x^13 -60*x^14 -28*x^17 +28*x^18)/((1-x)*(1-10*x^7)). - _David Radcliffe_, Jan 29 2016
%t A216261 Drop[#, 2] &@ CoefficientList[Series[(x^2 + 6 x^3 - 3 x^4 - 2 x^5 - 2 x^6 + 8 x^7 + 2 x^8 - 2 x^9 - 56 x^10 + 28 x^11 + 28 x^12 + 60 x^13 - 60 x^14 - 28 x^17 + 28 x^18)/((1 - x) (1 - 10 x^7)), {x, 0, 50}], x] (* _Michael De Vlieger_, Jan 29 2016 *)
%o A216261 (Haskell)
%o A216261 import Data.Maybe (fromJust)
%o A216261 import Data.List (elemIndex)
%o A216261 a216261 = fromJust . (`elemIndex` a006942_list)
%o A216261 -- _Reinhard Zumkeller_, Mar 15 2013
%o A216261 (PARI) Vec((x^2 +6*x^3 -3*x^4 -2*x^5 -2*x^6 +8*x^7 +2*x^8 -2*x^9 -56*x^10 +28*x^11 +28*x^12 +60*x^13 -60*x^14 -28*x^17 +28*x^18)/((1-x)*(1-10*x^7)) + O(x^50)) \\ _Michel Marcus_, Jan 29 2016
%Y A216261 Cf. A006942, A010371, A063720, A074458, A277116; A234691, A234692.
%Y A216261 Cf. A038619 and A143617 (identical up to initial terms).
%K A216261 nonn,base
%O A216261 2,2
%A A216261 _Reinhard Zumkeller_, Mar 15 2013
%E A216261 Name and cross-references edited by _M. F. Hasler_, Jun 17 2020