A080789 - OEIS

%I #7 Nov 19 2021 10:10:38

%S 11,19,61,68,101,109,110,116,118,161,166,169,181,188,190,199,601,608,

%T 610,616,619,661,680,1006,1010,1018,1019,1061,1066,1081,1090,1091,

%U 1096,1100,1106,1108,1109,1118,1160,1169,1180,1181,1186,1601,1606,1609,1610,1618

%N Numbers that are primes when turned upside down.

%D P. Giannopoulos, The Brainteasers (unpublished)

%H Michael S. Branicky, <a href="/A080789/b080789.txt">Table of n, a(n) for n = 1..10000</a>

%o (Python)

%o from sympy import isprime

%o from itertools import product

%o def ud(s):

%o     return s[::-1].translate({ord('6'):ord('9'), ord('9'):ord('6')})

%o def auptod(maxdigits):

%o     alst = []

%o     for d in range(1, maxdigits+1):

%o         for start in "16":

%o             for p in product("01689", repeat=d-1):

%o                 s = start + "".join(p)

%o                 t, udt = int(s), int(ud(s))

%o                 if isprime(udt): alst.append(t)

%o     return alst

%o print(auptod(4)) # _Michael S. Branicky_, Nov 19 2021

%Y Cf. A057770, A054047, A080788.

%K base,easy,nonn

%O 1,1

%A P. Giannopoulos (pgiannop1(AT)yahoo.com), Mar 12 2003

%E 610 inserted and a(24) and beyond from _Michael S. Branicky_, Nov 19 2021