cp's OEIS Frontend

A066918 a(n) = least natural number k such that f(k) begins a maximal zigzag of length n in the prime gaps function f(x) = p(x+1)-p(x), where p(x) denotes the x-th prime. (Cf. A066485.)

%I A066918 #7 Jun 24 2014 01:08:19
%S A066918 13,17,9,4,41,30,293,166,484,796,134,12209,1646,467,4673,763,1573,
%T A066918 7279,37989,153772,102051,377198,593191,41552,677313,473395,557448,
%U A066918 5536093,1643927,22986338,1877982,14184432,14828672,23278807,45383008,82020263
%N A066918 a(n) = least natural number k such that f(k) begins a maximal zigzag of length n in the prime gaps function f(x) = p(x+1)-p(x), where p(x) denotes the x-th prime. (Cf. A066485.)
%C A066918 A zigzag of a function f(n) is a run of consecutive strict local extrema.
%e A066918 f(11),f(12),...,f(15) are: 6, 4, 2, 4, 6. Note that a zigzag of length 1 occurs at f(13)=2. This is a maximal zigzag, since neither f(12)=4 nor f(14)=4 are local extrema of f. Also, a maximal zigzag of length 1 first occurs at f(13). Therefore a(1) = 13.
%t A066918 f[n_] := Prime[n+1]-Prime[n]; e[n_] := (f[n]-f[n-1])(f[n]-f[n+1])>0; For[n=1, n<100, n++, a[n]=0]; For[k=4; l=0, True, k++, If[e[k], l++, If[a[l]===0, Print["a(", l, ")=", a[l]=k-l]]; l=0]]
%Y A066918 Cf. A066485.
%K A066918 nonn
%O A066918 1,1
%A A066918 _Joseph L. Pe_, Jan 23 2002
%E A066918 Edited by _Dean Hickerson_, Jun 26 2002