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

1,1

Links

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

Example

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

Mathematica

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

Prog

(PARI) is(n)=my(r=fromdigits(Vecrev(digits(n)))); n<r && !isprime(n) && !isprime(r) && bigomega(n)==bigomega(r) \\ Charles R Greathouse IV, Oct 17 2018

Crossrefs

Cf. A050699, A050701.

Sequence in context: A032609 A050699 A097393 * A263108 A274182 A139566

Adjacent sequences: A050697 A050698 A050699 * A050701 A050702 A050703

Keyword

nonn,base

Author

Patrick De Geest, Aug 15 1999

Extensions

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

Status

approved