A075815 Palindromic odd composite numbers with an odd number of prime factors (counted with multiplicity).

99, 171, 333, 343, 363, 555, 575, 595, 747, 777, 909, 969, 1001, 1221, 1331, 1551, 1771, 3333, 3553, 5335, 5445, 5555, 5665, 5775, 5885, 5995, 7337, 7557, 7667, 7777, 7887, 9009, 9339, 9559, 9669, 9779, 9889, 11211, 11511, 11711, 11811, 12121

Offset: 1

Author

Jani Melik, Oct 13 2002

Keywords

• nonn
• base

Examples

			5445=3^2*5*11^2 and 5555=5*11*101 are palindromic, odd, composite and have an odd number of prime factors.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A046389.

Programs

Maple

test := proc(n) local d; d := convert(n,base,10); return ListTools[Reverse](d)=d and type(numtheory[bigomega](n),odd) and not isprime(n); end; a := []; for n from 1 to 13000 by 2 do if test(n) then a := [op(a),n]; end; od; a;

Mathematica

Select[Range[9,13000,2],PalindromeQ[#]&&CompositeQ[#]&&OddQ[ PrimeOmega[ #]]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 28 2021 *)

Extensions

Edited by Dean Hickerson, Oct 21 2002