A209929 - OEIS

%I #19 Dec 07 2017 09:49:13

%S 1,1,1,1,1,1,1,1,1,0,1,1,1,1,1,1,1,1,1,0,1,1,1,1,1,1,1,1,1,0,1,1,1,1,

%T 1,1,1,1,1,0,1,1,1,1,1,1,1,1,1,0,1,1,1,1,1,1,1,1,1,0,1,1,1,1,1,1,1,1,

%U 1,0,1,1,1,1,1,1,1,1,1,0,1,1,1,1,1,1,1,1,1,0,1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,0

%N Smallest digit of all divisors of n.

%C Also smallest digit of concatenation of all divisors  of n (A037278, A176558).

%C Also characteristic function of numbers n such that smallest digit among all divisors of n is 1 (A209931), in other words, numbers whose divisor set does not contain any number with a nonleading zero.

%C Sequence is not the same as A168184, first deviation is at a(101): A168184(101) = 1, a(101) = 0.

%C Sequence is not the same as A168046, first deviation is at a(214): A168046(214) = 1, a(214) = 0.

%H Antti Karttunen, <a href="/A209929/b209929.txt">Table of n, a(n) for n = 1..16384</a>

%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>

%e a(214) = 0 because smallest digit of all divisors of 214 (1, 2, 107, 214) is 0.

%t Table[Min[Flatten[IntegerDigits/@Divisors[n]]],{n,100}] (* _Harvey P. Dale_, Jul 20 2015 *)

%o (PARI)

%o A168046(n) = if(!n,0,!!(vecsort(digits(n),,8)[1]));

%o A209929(n) = { my(divs=divisors(n)); factorback(vector(numdiv(n),i,A168046(divs[i]))); }; \\ _Antti Karttunen_, Dec 07 2017

%Y Cf. A168046, A209928 (largest digit of all divisors of n), A054054 (smallest digit of n).

%K nonn,base,less

%O 1

%A _Jaroslav Krizek_, Mar 20 2012

%E More terms from _Antti Karttunen_, Dec 07 2017