A105179 - OEIS

%I #14 Nov 21 2013 12:48:40

%S 1,11,15,20,25,31,40,41,45,60,61,71,75,80,100,101,105,120,121,125,131,

%T 135,140,143,151,160,165,175,180,181,187,191,195,200,209,211,220,225,

%U 240,241,251,253,255,260,271,275,280,281,285,300,311,315,319,320,325

%N Numbers having in decimal representation the same final digit as their largest proper divisor has; a(1) = 1.

%C A010879(A032742(a(n))) = A010879(a(n));

%C A008602 is a subsequence apart from the initial term;

%C A030430 is a subsequence.

%H Reinhard Zumkeller, <a href="/A105179/b105179.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Fi#final">Index entries for sequences related to final digits of numbers</a>

%e n=105=3*35 and 105 == 35 modulo 10, therefore 105 is a term.

%t Join[{1},Select[Range[2,400],Last[IntegerDigits[Divisors[#][[-2]]]] == Last[IntegerDigits[#]]&]]  (* _Harvey P. Dale_, Apr 21 2011 *)

%o (PARI) lpf(n)=factor(n)[1,1]

%o is(n)=if(n%2, n%15==0||n%25==0||n==1||lpf(n)%5==1, n%20==0) \\ _Charles R Greathouse IV_, Jan 02 2013

%o (Haskell)

%o a105179 n = a105179_list !! (n-1)

%o a105179_list = 1 : filter (\x -> a010879 (a032742 x) == a010879 x) [2..]

%o -- _Reinhard Zumkeller_, Jan 10 2013

%K nonn,base

%O 1,2

%A _Reinhard Zumkeller_, Apr 29 2005