A109848 Highest common factor of n and its 9's complement.
1, 1, 3, 1, 1, 3, 1, 1, 9, 1, 11, 3, 1, 1, 3, 1, 1, 9, 1, 1, 3, 11, 1, 3, 1, 1, 9, 1, 1, 3, 1, 1, 33, 1, 1, 9, 1, 1, 3, 1, 1, 3, 1, 11, 9, 1, 1, 3, 1, 1, 3, 1, 1, 9, 11, 1, 3, 1, 1, 3, 1, 1, 9, 1, 1, 33, 1, 1, 3, 1, 1, 9, 1, 1, 3, 1, 11, 3, 1, 1, 9, 1, 1, 3, 1, 1, 3, 11, 1, 9, 1, 1, 3, 1, 1, 3, 1, 1, 99, 1, 1, 3
Offset: 1
Examples
a(55)=11 because the 9's complement of 55 is 99 - 55 = 44 and the greatest common divisor of 44 and 55 is 11.
Links
- Harvey P. Dale, Table of n, a(n) for n = 1..1000
Programs
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Maple
digs := proc(inp::integer) local resul,shiftinp : resul := 1 : shiftinp := iquo(inp,10) : while shiftinp > 0 do resul := resul+1 : shiftinp := iquo(shiftinp,10) : od : RETURN(resul) : end: nin := proc(inp::integer) RETURN(10^digs(inp)-1-inp) : end : for n from 1 to 80 do comp := nin(n) ; #print(n,comp,gcd(n,comp)) ; printf("%d,",gcd(n,comp)) ; od : # R. J. Mathar, Mar 27 2006 -
Mathematica
hcf[n_]:=Module[{idn=IntegerDigits[n],c9},c9=FromDigits[PadRight[{}, Length[idn],9]-idn];GCD[n,c9]]; Array[hcf,110] (* Harvey P. Dale, Dec 18 2012 *)
Extensions
Corrected and extended by R. J. Mathar, Mar 27 2006
More terms from Joshua Zucker, May 03 2006