|
|
A050701
|
|
If composite k and its reverse are different and have same number of prime factors, then the larger of them is a term of the sequence.
|
|
2
|
|
|
51, 62, 85, 93, 94, 221, 302, 321, 341, 381, 413, 442, 492, 493, 502, 511, 513, 514, 522, 524, 533, 534, 551, 553, 561, 562, 574, 581, 582, 604, 605, 621, 622, 623, 642, 663, 682, 685, 705, 711, 723, 734, 741, 766, 771, 781, 794, 805, 814, 817
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
EXAMPLE
|
a(n)=341 -> reverse(a(n)) = 143 gives the pair (143,341) of which only the larger value 341 is retained.
|
|
MATHEMATICA
|
rev[n_]:=FromDigits[Reverse[IntegerDigits[n]]]; Select[Range[825], !PrimeQ[#]&&PrimeOmega[#]==PrimeOmega[x=rev[#]]&&#>x&] (* Jayanta Basu, May 31 2013 *)
|
|
PROG
|
(PARI) isok(m) = my(k=fromdigits(Vecrev(digits(m)))); (m%10) && !isprime(m) && (m>k) && (bigomega(k) == bigomega(m)); \\ Michel Marcus, Aug 18 2021
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,base
|
|
AUTHOR
|
|
|
EXTENSIONS
|
Revised by Editors of OEIS, Oct 19 2019
Incorrect 394 and 523 removed and name clarified by Sean A. Irvine, Aug 17 2021
|
|
STATUS
|
approved
|
|
|
|