A080789 Numbers that are primes when turned upside down.

11, 19, 61, 68, 101, 109, 110, 116, 118, 161, 166, 169, 181, 188, 190, 199, 601, 608, 610, 616, 619, 661, 680, 1006, 1010, 1018, 1019, 1061, 1066, 1081, 1090, 1091, 1096, 1100, 1106, 1108, 1109, 1118, 1160, 1169, 1180, 1181, 1186, 1601, 1606, 1609, 1610, 1618

Offset: 1

Author

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

Keywords

• base
• easy
• nonn

References

• P. Giannopoulos, The Brainteasers (unpublished)

Links

• Michael S. Branicky, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A057770, A054047, A080788.

Programs

Python

from sympy import isprime
from itertools import product
def ud(s):
    return s[::-1].translate({ord('6'):ord('9'), ord('9'):ord('6')})
def auptod(maxdigits):
    alst = []
    for d in range(1, maxdigits+1):
        for start in "16":
            for p in product("01689", repeat=d-1):
                s = start + "".join(p)
                t, udt = int(s), int(ud(s))
                if isprime(udt): alst.append(t)
    return alst
print(auptod(4)) # Michael S. Branicky, Nov 19 2021

Extensions

610 inserted and a(24) and beyond from Michael S. Branicky, Nov 19 2021