A226090 - OEIS

%I #19 May 10 2014 09:51:21

%S 27,343,729,1331,2197,6859,29791,50653,59319,103823,185193,226981,

%T 250047,389017,456533,704969,804357,2048383,2352637,3869893,5000211,

%U 5929741,9393931,11697083,13312053,13651919,14348907,15813251,19034163,20346417,24642171,27818127

%N Cubes that become prime when their most significant (or leftmost) digit is removed.

%C This is to A225873 as cubes A000578 are to squares A000290.

%H Christian N. K. Anderson, <a href="/A226090/b226090.txt">Table of n, a(n) for n = 1..10000</a>

%e a(1) = 27 because removing the leftmost digit gives 7, a prime.

%e a(8) = 50653 because removing the leftmost digit gives 0653 = 653, which is prime.

%e a(21) = 5000211 because removing the leftmost digit gives 000211 = 00211 = 0211 = 211, which is prime.

%o (R) library(gmp); no0<-function(s){ while(substr(s,1,1)=="0" & nchar(s)>1) s=substr(s,2,nchar(s)); s}; trimL=function(x) { x=as.character(x); ifelse(nchar(x)<2,0,no0(substr(x,2,nchar(x)))) }; y=as.bigz(rep(0,10000)); len=0; n=as.bigz(-1); while(len<10000) if(isprime(trimL((n=n+1)^3))) {y[(len=len+1)]=n^3; if(len%%100==0) cat(len,as.character(y[len]),"\n") }

%o (PARI) for(n=3,1e3,t=Vec(Str(n^3));if(isprime(eval(concat(t[2..#t]))),print1(n^3", "))) \\ _Charles R Greathouse IV_, Jun 10 2013

%Y Cf. A000578, A225873.

%K nonn,easy,base

%O 1,1

%A _Jonathan Vos Post_, May 25 2013