%I #18 Nov 18 2022 15:10:16

%S 11,171,1771,17771,177771,1777771,17777771,177777771,1777777771,

%T 17777777771,177777777771,1777777777771,17777777777771,

%U 177777777777771,1777777777777771,17777777777777771,177777777777777771,1777777777777777771,17777777777777777771

%N a(n)=n 7's sandwiched between two 1's.

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).

%F a(0)=1, a(n) = 10*a(n-1)+61.

%F a(n) = (160*10^n-61)/9 (see PARI's code by Charles R Greathouse IV).

%t a[0]=11;a[n_]:=a[n-1]*10+61;Table[a[n],{n,0,44}]

%t Table[10 FromDigits[PadRight[{1},n,7]]+1,{n,20}] (* _Harvey P. Dale_, Nov 18 2022 *)

%o (PARI) a(n)=(160*10^n-61)/9 \\ _Charles R Greathouse IV_, Jan 23 2012

%K nonn,easy,less,base

%O 0,1

%A _José María Grau Ribas_, Jan 22 2012