|
|
A103741
|
|
a(n) is a non-palindromic composite located between twin primes whose reverse, which is less than it, is also located between twin primes.
|
|
3
|
|
|
60, 240, 270, 600, 810, 822, 2130, 2340, 2802, 8010, 8220, 8430, 8838, 8862, 20550, 22740, 23202, 23370, 23910, 25410, 26880, 27240, 28410, 28572, 28662, 29022, 29760, 80472, 81702, 81930, 81972, 82140, 82530, 83220, 83340, 83640, 85620
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
EXAMPLE
|
810 is in the sequence as it is between the twin primes 809 and 811 and its reverse, 018 or 18, is also between the twin primes 17 and 19.
|
|
MATHEMATICA
|
fQ[n_] := Block[{np = FromDigits[ Reverse[ IntegerDigits[n]]]}, If[np < n && PrimeQ[n - 1] && PrimeQ[n + 1] && PrimeQ[np - 1] && PrimeQ[np + 1], True, False]]; Select[ Range[2, 87220, 2], fQ[ # ] &] (* Robert G. Wilson v, Mar 30 2005 *)
npcQ[n_]:=Module[{ridn=FromDigits[Reverse[IntegerDigits[n]]]}, ridn<n && And@@PrimeQ[ {ridn-1, ridn+1}]]; Select[Mean/@Select[Partition[ Prime[ Range[ 2, 8500]], 2, 1], Last[#]-First[#]==2&], npcQ] (* Harvey P. Dale, Oct 19 2012 *)
|
|
CROSSREFS
|
|
|
KEYWORD
|
base,nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|