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 A186438 #37 Nov 24 2024 21:00:03
%S A186438 10,12,20,30,38,40,50,60,62,70,80,88,90,100,110,112,120,130,138,140,
%T A186438 150,160,162,170,180,188,190,200,210,212,220,230,238,240,250,260,262,
%U A186438 270,280,288,290,300,310,312,320,330,338,340,350,360,362,370,380,388,390,400,410,412
%N A186438 Positive numbers whose squares end in two identical digits.
%C A186438 The numbers are of the form : 10k, or 50k - 12, or 50k + 12, or 50k + 38.
%D A186438 Jean Meeus, Letter to N. J. A. Sloane, Dec 26 1974.
%H A186438 J. Meeus & N. J. A. Sloane, <a href="/A006532/a006532_1.pdf">Correspondence, 1974-1975</a>
%H A186438 Ana Rechtman, <a href="http://images-archive.math.cnrs.fr/Juillet-2021-4e-defi.html">Juillet 2021, 4e défi</a>, Images des Mathématiques, CNRS, 2021 (in French).
%H A186438 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,0,1,-1).
%F A186438 G.f.: 2*x*(5*x^6+x^5+4*x^4+5*x^3+4*x^2+x+5)/((x-1)^2 * (x^6+x^5+x^4+x^3+x^2+x+1)). [_Colin Barker_, Jul 02 2012]
%e A186438 62 is in the sequence because 62^2 = 3844.
%p A186438 with(numtheory):T:=array(1..10):for p from 1 to 1000 do:n:=p^2:l:=length(n):n0:=n:for
%p A186438 m from 1 to l do:q:=n0:u:=irem(q,10):v:=iquo(q,10):n0:=v :T[m]:=u:od:if T[1]=T[2]
%p A186438 then printf(`%d, `,p):else fi:od:
%t A186438 tidQ[n_]:=Module[{idn=IntegerDigits[n^2]},idn[[-1]]==idn[[-2]]]; Select[ Range[ 4,500],tidQ] (* or *) LinearRecurrence[{1,0,0,0,0,0,1,-1},{10,12,20,30,38,40,50,60},60] (* _Harvey P. Dale_, Jan 25 2014 *)
%Y A186438 Cf. A016742 (even squares), A123912.
%K A186438 nonn,base,easy
%O A186438 1,1
%A A186438 _Michel Lagneau_, Feb 21 2011