A108849 - OEIS

%I #12 Apr 03 2024 05:06:33

%S 4,9,46,94,121,169,215,526,961,982,1042,1273,1405,1843,2918,3194,4069,

%T 4633,5213,5221,6313,6511,6937,8402,9235,9481,9586,9886,10201,10609,

%U 12538,12769,14023,16171,16327,16582,16723,18085,18463,18811,27845

%N Semiprimes whose digit reversal is a nontrivial power.

%C Some nonsquare brilliant numbers in the sequence: 70597 = 227*311 (79507 = 43^3), 76121 = 163*467 (12167 = 23^3), 211591 = 457*463 (195112 = 58^3), 291149 = 359*811 (941192 = 98^3) ...

%H Chai Wah Wu, <a href="/A108849/b108849.txt">Table of n, a(n) for n = 1..14430</a>

%e 215 is a term because 215 = 5*43 and 512 = 2^9.

%t Revfn[n_]:=FromDigits[Reverse[IntegerDigits[n]]];Select[Range[30000],Revfn[#]>1&&PrimeOmega[#]==2&&ResourceFunction["PerfectPowerQ"][Revfn[#]]&] (* _James C. McMahon_, Apr 02 2024 *)

%o (PARI) isok(n) = (bigomega(n)==2) && ispower(subst(Polrev(digits(n)), x, 10)); \\ _Michel Marcus_, Jun 03 2016

%Y Cf. A069798.

%K base,nonn

%O 1,1

%A _Jason Earls_, Jul 11 2005