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A050700
Composite numbers n smaller than their decimal reverse but having the same number of prime factors.
4
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
Sequence in context: A032609 A050699 A097393 * A373731 A263108 A274182
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