A181639 Numbers n such that omega(n) = digit-reverse(n).

20, 30, 200, 300, 2000, 3000, 20000, 30000, 200000, 300000, 2000000, 3000000, 20000000, 30000000

Offset

1,1

Comments

omega(n) = A001221(n) is the number of distinct primes dividing n.

Links

Table of n, a(n) for n=1..14.

Formula

{n: A001221(n) = A004086(n)}

Example

300 is in the sequence because omega(300) = reversal(300) = 3.

Mathematica

Do[If[Length[ FactorInteger[ n ]]==FromDigits[Reverse[IntegerDigits[n]]], Print[n]],
  {n, 1, 10^9}]
Select[Range[10^9], PrimeNu[#]==FromDigits[Reverse[IntegerDigits[#]]]&] (* or *) Flatten[Table[{2*10^n, 3*10^n}, {n, 10}]] (* Harvey P. Dale, Dec 17 2013 *)

Crossrefs

Cf. A001221.

Sequence in context: A066214 A285494 A120210 * A166631 A167360 A113760

Adjacent sequences: A181636 A181637 A181638 * A181640 A181641 A181642

Keyword

nonn,base

Author

Michel Lagneau, Nov 18 2010

Status

approved