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 A246561 Least number k such that k concatenated with n is a cube, or 0 if no such k exists. 0

%I

%S 133,51,34,6,12,21,2,172,72,0,3579,5,49,0,0,2,3890,0,593,0,689,0,1038,

%T 138,1,0,0,17,0,0,13,58,4565,0,0,973,359,0,4930,0,5314,0,0,27,0,0,

%U 2500,106,1176,0,1326,219,506,0,0,466,8043,0,68,0,92,0,3007,1574,0,0,121,327,7049,0,7535,548,9126,0,33

%N Least number k such that k concatenated with n is a cube, or 0 if no such k exists.

%C a(n) = 0 if and only if n is in A246449.

%e 512 is the smallest cube ending with digit 2, so a(2) = 51.

%o (PARI)

%o b(n)=v=[];for(k=10^(n-1),10^n,v=concat(v,k^3%10^n));v=vecsort(v,,8);v

%o w=[];for(k=1,250,d=digits(k);if(vecsearch(b(#d),k),w=concat(w,k)));w=vecsort(w,,8);w;

%o a(n)=if(!vecsearch(w,n),return(0));if(vecsearch(w,n),j=1;s=Str(n);while(!ispower(eval(concat(Str(j),s)),3),j++);return(j))

%o vector(200,n,a(n))

%Y Cf. A000578, A246449, A245631.

%K nonn,base

%O 1,1

%A _Derek Orr_, Aug 29 2014

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Last modified May 8 13:26 EDT 2021. Contains 343666 sequences. (Running on oeis4.)