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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 Cf. A006567, A134941, A134951, A135417, A173071. Sequence in context: A250894 A251405 A278018 * A183881 A270540 A206272 Adjacent sequences: A182718 A182719 A182720 * A182722 A182723 A182724 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.)