A050700 Composite numbers n smaller than their decimal reverse but having the same number of prime factors.

15, 26, 39, 49, 58, 115, 117, 122, 123, 126, 129, 143, 147, 155, 158, 159, 165, 169, 177, 178, 183, 185, 187, 203, 205, 225, 226, 244, 246, 265, 285, 286, 289, 294, 314, 315, 319, 326, 327, 329, 335, 338, 339, 355, 366, 369, 394, 398, 406, 415, 418, 425

Offset: 1

Author

Patrick De Geest, Aug 15 1999

Keywords

• nonn
• base

Examples

			a(n)=143 -> a(n)-reversed=341 gives pair (143,341) of which only the smaller value 143 is in this sequence.
		

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A050699, A050701.

Programs

Mathematica

rev[n_]:=FromDigits[Reverse[IntegerDigits[n]]]; Select[Range[425],!PrimeQ[#]&&PrimeOmega[#]==PrimeOmega[x=rev[#]]&&#Jayanta Basu, May 31 2013 *)

PARI

is(n)=my(r=fromdigits(Vecrev(digits(n)))); nCharles R Greathouse IV, Oct 17 2018

Extensions

Name edited and offset corrected by Charles R Greathouse IV, Oct 17 2018