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A182721 Mountain emirps. 2
1231, 1321, 1381, 1471, 1741, 1831, 12491, 12641, 12841, 13591, 13751, 13781, 13841, 14591, 14621, 14821, 14831, 14891, 15731, 15791, 18731, 19421, 19531, 19541, 19751, 19841, 123731, 123821, 124951, 124981, 125641, 125651, 125791, 125821, 125941, 126761, 126851 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Intersection of emirps A006567 and mountain numbers A134941.
The smallest mountain emirp 1231 and other terms of this sequence was mentioned by Loungrides in Prime Curios! (see link).
Question: How many are there?
There are 602 such terms. - Michael S. Branicky, Dec 31 2021
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..602 (full sequence)
G. L. Honaker, Jr. and C. K. Caldwell, Prime Curios! 1231
FORMULA
A006567 INTERSECT A134941.
EXAMPLE
Illustration of a(11) = 13751 as a mountain emirp:
. . . . .
. . . . .
. . 7 . .
. . . . .
. . . 5 .
. . . . .
. 3 . . .
. . . . .
1 . . . 1
PROG
(Python) # uses A134941()
from sympy import isprime
def is_emirp(n):
if not isprime(n): return False
revn = int(str(n)[::-1])
return n != revn and isprime(revn)
print([k for k in A134941() if is_emirp(k)]) # Michael S. Branicky, Dec 31 2021
CROSSREFS
Sequence in context: A250894 A251405 A278018 * A183881 A270540 A206272
KEYWORD
nonn,base,fini,full
AUTHOR
Omar E. Pol, Dec 21 2010
EXTENSIONS
More terms from Nathaniel Johnston, Dec 29 2010
Terms a(31) and beyond from Michael S. Branicky, Dec 31 2021
STATUS
approved

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Last modified June 25 05:27 EDT 2024. Contains 373697 sequences. (Running on oeis4.)