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

Author

Amarnath Murthy, Jul 06 2005

Keywords

• base
• easy
• nonn

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

Crossrefs

Cf. A109847, A084021.

Programs

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