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

1,1

Links

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

Example

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

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 *)

Crossrefs

Cf. A046389.

Sequence in context: A185498 A126230 A055164 * A075814 A320707 A235228

Adjacent sequences: A075812 A075813 A075814 * A075816 A075817 A075818

Keyword

nonn,base

Author

Jani Melik, Oct 13 2002

Extensions

Edited by Dean Hickerson, Oct 21 2002

Status

approved