cp's OEIS Frontend

A108896 Numbers whose outer two digits are 9's and inner digits are 4's.

%I A108896 #30 Jul 31 2022 23:11:10
%S A108896 949,9449,94449,944449,9444449,94444449,944444449,9444444449,
%T A108896 94444444449,944444444449,9444444444449,94444444444449,
%U A108896 944444444444449,9444444444444449,94444444444444449,944444444444444449,9444444444444444449,94444444444444444449
%N A108896 Numbers whose outer two digits are 9's and inner digits are 4's.
%C A108896 All terms are composite.
%C A108896 From _Sergio Pimentel_, Jul 26 2022: (Start)
%C A108896 a(n) is divisible by:
%C A108896   13 if n == 1 (mod 6).
%C A108896   11 if n == 0,2,4 (mod 6).
%C A108896    3 if n == 0,3 (mod 6).
%C A108896    7 if n == 5 (mod 6). (End)
%H A108896 Cino Hilliard, <a href="https://web.archive.org/web/20080621164208/http://groups.msn.com/BC2LCC/94444449notprime.msnw">Proof 94..49</a>
%H A108896 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A108896 a(n) = 9*10^(n+1) + 9 + 40*(10^n-1)/9.
%F A108896 From _Chai Wah Wu_, Jul 27 2022: (Start)
%F A108896 a(n) = 11*a(n-1) - 10*a(n-2) for n > 2.
%F A108896 G.f.: x*(949 - 990*x)/((x - 1)*(10*x - 1)). (End)
%t A108896 Table[10*FromDigits[PadRight[{9},n,4]]+9,{n,2,20}] (* _Harvey P. Dale_, Apr 02 2018 *)
%o A108896 (PARI) S(n,r,m)=for(x=1,n,y=m*10^(x+1)+m+r*10*(10^x-1)/9;print1(y","))
%o A108896 (Python)
%o A108896 def a(n): return int('9' + '4'*n + '9')
%o A108896 print([a(n) for n in range(1, 19)]) # _Michael S. Branicky_, Jul 26 2022
%Y A108896 Cf. A108903, A108904.
%K A108896 easy,nonn,base
%O A108896 1,1
%A A108896 _Cino Hilliard_, Jul 16 2005