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

1,1

References

P. Giannopoulos, The Brainteasers (unpublished)

Links

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

Prog

(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

Crossrefs

Cf. A057770, A054047, A080788.

Sequence in context: A265802 A178385 A139602 * A057770 A080788 A363023

Adjacent sequences: A080786 A080787 A080788 * A080790 A080791 A080792

Keyword

base,easy,nonn

Author

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

Extensions

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

Status

approved