A050699 Nonprime numbers n such that n and n-reversed (<> n and no leading zeros) have the same number of prime factors (counted with multiplicity).
15, 26, 39, 49, 51, 58, 62, 85, 93, 94, 115, 117, 122, 123, 126, 129, 143, 147, 155, 158, 159, 165, 169, 177, 178, 183, 185, 187, 203, 205, 221, 225, 226, 244, 246, 265, 285, 286, 289, 294, 302, 314, 315, 319, 321, 326, 327, 329, 335, 338, 339, 341, 355, 366
Offset: 1
Examples
E.g., 321 = 3*107 and 123 = 3*41 -> both 321 and 123 have two prime factors.
Links
- Nathaniel Johnston, Table of n, a(n) for n = 1..10000
Programs
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Maple
with(numtheory): read(transforms): for n from 12 to 366 do r:=digrev(n): if(not isprime(n) and not n=r and not n mod 10 = 0 and bigomega(n)=bigomega(r))then printf("%d, ", n); fi: od: # Nathaniel Johnston, Jun 23 2011 -
Mathematica
nrnQ[n_]:=Module[{idn=IntegerDigits[n],rev},rev=Reverse[idn];!PrimeQ[n] &&First[rev]!=0&&idn!=rev&&PrimeOmega[n]==PrimeOmega[FromDigits[rev]]]; Select[Range[400],nrnQ] (* Harvey P. Dale, Jun 23 2011 *)
Extensions
Definition clarified by Harvey P. Dale, Jun 23 2011