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%I #11 Dec 15 2017 17:35:38
%S 1,1,1,1,2,3,5,10,19,38,76,152,303,605,1210,2420,4839,9678,19355,
%T 38709,77417,154834,309667,619333,1238665,2477330,4954660,9909319,
%U 19818638,39637275,79274549
%N Number of decimal digits in A001042.
%t a[ 1 ] = 1; a[ 2 ] = 2; a[ n_ ] := a[ n ] = a[ n - 1 ]^2 - a[ n - 2 ]^2; Table[ Floor[ N[ Log[ 10, a[ n ] ], 36 ] ] + 1, {n, 1, 31} ]
%t IntegerLength[#]&/@(RecurrenceTable[{a[1]==1,a[2]==2,a[n]==a[n-1]^2- a[n-2]^2},a,{n,31}]) (* _Harvey P. Dale_, Dec 27 2013 *)
%o (PARI) a(n) = if(n<2,n+1,a(n-1)^2-a(n-2)^2); l(n) = ln=0; while(n,n=floor(n/10); ln++); return(ln); for(n=0,21,print(l(a(n))))
%o (Haskell)
%o a064236 = length . show . a001042 -- _Reinhard Zumkeller_, Dec 16 2013
%K base,nonn
%O 0,5
%A _Jason Earls_, Sep 22 2001
%E More terms from _Robert G. Wilson v_, Sep 24 2001
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