A108849 Semiprimes whose digit reversal is a nontrivial power.

4, 9, 46, 94, 121, 169, 215, 526, 961, 982, 1042, 1273, 1405, 1843, 2918, 3194, 4069, 4633, 5213, 5221, 6313, 6511, 6937, 8402, 9235, 9481, 9586, 9886, 10201, 10609, 12538, 12769, 14023, 16171, 16327, 16582, 16723, 18085, 18463, 18811, 27845

Offset

1,1

Comments

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) ...

Links

Chai Wah Wu, Table of n, a(n) for n = 1..14430

Example

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

Mathematica

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

Prog

(PARI) isok(n) = (bigomega(n)==2) && ispower(subst(Polrev(digits(n)), x, 10)); \\ Michel Marcus, Jun 03 2016

Crossrefs

Cf. A069798.

Sequence in context: A024053 A197970 A048892 * A375910 A025558 A298986

Adjacent sequences: A108846 A108847 A108848 * A108850 A108851 A108852

Keyword

base,nonn

Author

Jason Earls, Jul 11 2005

Status

approved