A054518 - OEIS

%I #15 Oct 31 2022 15:23:31

%S 10,12,15,18,21,24,25,26,27,28,36,39,40,42,45,46,48,49,51,52,54,56,57,

%T 58,60,62,63,64,65,68,69,72,75,78,80,81,82,84,85,86,87,90,93,94,96,

%U 100,102,105,108,114,115,116,117,120

%N Emirpnons (nonprimes whose reversal is a different nonprime).

%H Harvey P. Dale, <a href="/A054518/b054518.txt">Table of n, a(n) for n = 1..1001</a>

%e a(1)=12 because 12 is not a prime, neither is 21 and 12<>21

%t emirpnonQ[n_]:=Module[{idn=IntegerDigits[n],ridn},ridn=Reverse[idn];n>9&&ridn!=idn&&!PrimeQ[FromDigits[ridn]]]; With[{nprs=Complement[ Range[ 120], Prime[ Range[PrimePi[120]]]]},Select[nprs,emirpnonQ]] (* _Harvey P. Dale_, Feb 05 2012 *)

%o (Python)

%o from sympy import isprime

%o def ok(n):

%o     r = int(str(n)[::-1])

%o     if r == n: return False

%o     return not isprime(n) and not isprime(r)

%o print([k for k in range(121) if ok(k)]) # _Michael S. Branicky_, Oct 24 2022

%Y Cf. A006567.

%K base,easy,nonn

%O 1,1

%A _Henry Bottomley_, Apr 07 2000

%E Offset corrected by _Sean A. Irvine_, Oct 24 2022