A049110 - OEIS

%I #10 Nov 07 2018 21:46:34

%S 6,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,12,8,8,8,8,8,8,8,8,

%T 8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,12,8,8,8,

%U 8,8,12,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8

%N Number of divisors of A006601(n).

%H Antti Karttunen, <a href="/A049110/b049110.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A000005(A006601(n)).

%t With[{s = DivisorSigma[0, Range[10^5]]}, s[[SequencePosition[s, {x_, x_, x_, x_}][[All, 1]] ]] ] (* _Michael De Vlieger_, Nov 07 2018, after _Harvey P. Dale_ at A006601 *)

%o (PARI)

%o up_to = 10000;

%o A049110list(up_to) = { my(v=vector(up_to),t,n=1,i=0); while(i<up_to,t = numdiv(n); if(numdiv(n+1)==t && numdiv(n+2)==t && numdiv(n+3)==t, i++; v[i] = t); n++); (v); }

%o v049110 = A049110list(up_to);

%o A049110(n) = v049110[n]; \\ _Antti Karttunen_, Nov 07 2018

%o (PARI) upto(n) = my(res = List(), current = 1, c, streak = 1); for(i = 2, n + 3, c = numdiv(i); if(c == current, streak++; if(streak == 4, listput(res, c)), streak = 1; current = c)); res \\ _David A. Corneth_, Nov 07 2018

%Y Cf. A000005, A006601.

%K nonn

%O 1,1

%A _Olivier Gérard_