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A281131 First appearance of 2^n in A281130. 3

%I

%S 1,3,7,13,23,41,98,223,437,699,1213,2624,4674,11163,21300,40858,73977,

%T 148591,297394,567076,1100738,2243474,4340628,8726122,17397270,

%U 34701556,68372147,136254352,271069771,546613630,1088921640,2163138108,4334318825

%N First appearance of 2^n in A281130.

%C Conjecture: a(n) ~ 2^n.

%H Rok Cestnik, <a href="/A281131/a281131_2.c.txt">C program (utilizing hard drive memory)</a>

%e a(1) = 3 because A281130(3) = 2^1 and A281130(i) != 2^1 for i < 3.

%e a(2) = 7 because A281130(7) = 2^2 and A281130(i) != 2^2 for i < 7.

%t a[n_] := a[n] = If[a[n - 2] < a[n - 1], a[n - 1 - a[n - 1]], 2 a[n - 1]]; a[1] = a[2] = 1; Function[w, Function[e, First /@ Lookup[w, 2^e]]@ Range[0, Log2@ Max@ Keys@ w]]@ PositionIndex@ Array[a, 10^7] (* _Michael De Vlieger_, Jan 21 2017, Version 10. *)

%o (C)

%o #include<stdio.h>

%o #include<stdlib.h>

%o int main(void){

%o int N = 1000000000;

%o int *a = (int*)malloc((N+1)*sizeof(int));

%o int max = 1;

%o int maxindex = 1;

%o a[1] = 1;

%o a[2] = 1;

%o for(int i = 2; i < N; ++i){

%o if(a[i-1] < a[i]) a[i+1] = a[i-a[i]];

%o else a[i+1] = 2*a[i];

%o if(a[i+1] > max){

%o max = a[i+1];

%o printf("%d %d\n", maxindex, i+1);

%o maxindex++;

%o }

%o }

%o return 0;

%o }

%Y Cf. A281130, A291598.

%K nonn,hard

%O 0,2

%A _Rok Cestnik_, Jan 15 2017

%E a(31)-a(32) from _Rok Cestnik_, Aug 27 2017

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Last modified November 12 22:10 EST 2019. Contains 329079 sequences. (Running on oeis4.)