A046399 Smallest squarefree palindrome with exactly n distinct prime factors.

1, 2, 6, 66, 858, 6006, 222222, 22444422, 244868442, 6434774346, 438024420834, 50146955964105, 2415957997595142, 495677121121776594, 22181673755737618122, 5521159517777159511255, 477552751050050157255774

Offset: 0

Author

Patrick De Geest, Jun 15 1998

Keywords

• nonn
• base
• hard
• more

Comments

Initial terms of sequences A046392-A046398.

Examples

			a(4) = 858 = 2*3*11*13.
		

References

• J.-P. Delahaye, Merveilleux nombres premiers ("Amazing primes"), p. 315, Pour la Science, Paris 2000.

Crossrefs

Cf. A046385, A076886.

Cf. A046392, A046393, A046394, A046395, A046396, A046397, A046398.

Programs

Mathematica

r[n_] := FromDigits[Reverse[IntegerDigits[n]]]; Do[k = 1; While[r[k] != k || !SquareFreeQ[k] || Length[Select[Divisors[k], PrimeQ]] != n, k++ ]; Print[k], {n, 0, 30}] (* Ryan Propper, Sep 16 2005 *)

Extensions

Edited by N. J. A. Sloane, Dec 06 2008 at the suggestion of R. J. Mathar

a(10)-a(13) from Donovan Johnson, Oct 03 2011

a(14)-a(15) from David A. Corneth, Oct 03 2020

a(15) corrected by Daniel Suteu, Feb 05 2023

a(16) from Michael S. Branicky, Feb 08 2023