A054518 Emirpnons (nonprimes whose reversal is a different nonprime).

10, 12, 15, 18, 21, 24, 25, 26, 27, 28, 36, 39, 40, 42, 45, 46, 48, 49, 51, 52, 54, 56, 57, 58, 60, 62, 63, 64, 65, 68, 69, 72, 75, 78, 80, 81, 82, 84, 85, 86, 87, 90, 93, 94, 96, 100, 102, 105, 108, 114, 115, 116, 117, 120

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1001

Example

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

Mathematica

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 *)

Prog

(Python)
from sympy import isprime
def ok(n):
    r = int(str(n)[::-1])
    if r == n: return False
    return not isprime(n) and not isprime(r)
print([k for k in range(121) if ok(k)]) # Michael S. Branicky, Oct 24 2022

Crossrefs

Cf. A006567.

Sequence in context: A006793 A308268 A248715 * A072198 A057485 A162825

Adjacent sequences: A054515 A054516 A054517 * A054519 A054520 A054521

Keyword

base,easy,nonn

Author

Henry Bottomley, Apr 07 2000

Extensions

Offset corrected by Sean A. Irvine, Oct 24 2022

Status

approved