A072037 - OEIS

%I #15 Oct 31 2013 12:25:41

%S 4,8,9,121,343,1331,10201,14641,94249,1030301,104060401,

%T 900075181570009,10022212521222001,12124434743442121,

%U 12323244744232321,12341234943214321,1022321210249420121232201,1210024420147410244200121,1210222232227222322220121

%N Palindromic powers (with positive exponents) of a prime but not a prime (A025475).

%e E.g. 94249=307*307

%t a = {}; Do[pp = Prime[n]^i; d = IntegerDigits[pp]; If[d == Reverse[d], a = Append[a, pp]], {n, 1, PrimePi[ Sqrt[10^21]]}, {i, 2, Floor[ Log[ Prime[n], 10^21]]}]; Sort[a] (_Robert G. Wilson v_)

%o (PARI) {a=10^15; v=[]; m=sqrt(a); forprime(p=2,m,q=p; while((q=q*p)<a,n=q; rev=0; while(n>0,d=divrem(n,10); n=d[1]; rev=10*rev+d[2]); if(q==rev,v=concat(v,q)))); v=vecsort(v); for(j=1,matsize(v)[2],print1(v[j],","))}

%Y Cf. A025475, A002385.

%K base,easy,nonn

%O 1,1

%A _Labos Elemer_, Jun 07 2002

%E Two more term from _Klaus Brockhaus_, Jun 07 2002

%E Four more terms from _Robert G. Wilson v_, Oct 31 2002

%E Added a(17)-a(19), clarified definition, _Donovan Johnson_, Sep 01 2012