A263240 -id:A263240 - cp's OEIS frontend

A263242 Larger of emirp pairs that are merely reversals of their end digits.

31, 71, 73, 97, 311, 701, 733, 743, 751, 761, 907, 937, 941, 953, 967, 971, 983, 991, 3221, 9001, 9221, 9227, 9551, 9661, 9883, 32321, 33931, 34141, 34841, 35051, 36061, 36761, 37571, 39791, 70001, 71711, 72221, 73331, 74143, 74441, 74843, 74941, 75253, 76261, 76463, 76561

Offset: 1

Lekraj Beedassy, Oct 13 2015

The first digit is always larger than the last digit.

Harvey P. Dale, Table of n, a(n) for n = 1..500

Cf. A006567, A109309, A263240, A263241.

epQ[n_]:=Module[{idn=IntegerDigits[n],mid},mid=Rest[Most[idn]];PrimeQ[ IntegerReverse[n]]&&mid==Reverse[mid]&&idn[[1]]>idn[[-1]]]; Select[ Prime[Range[6,8000]],epQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Oct 10 2016 *)

Corrected by Harvey P. Dale, Oct 10 2016

A263241 Lesser of emirp pairs that are merely reversals of their end digits.

Original entry on oeis.org

13, 17, 37, 79, 107, 113, 149, 157, 167, 179, 199, 337, 347, 359, 389, 709, 739, 769, 1009, 1223, 1229, 1559, 1669, 3889, 7229, 10007, 10009, 10909, 11717, 11719, 12227, 12323, 12829, 13337, 13933, 14143, 14447, 14449, 14549, 14843, 14947, 15053, 16063, 16267, 16567, 16763

Offset: 1

Lekraj Beedassy, Oct 13 2015

The first digit is always smaller than last digit.

Cf. A006567, A109308, A263240, A263242.

Select[Range[20000], And @@ PrimeQ[{#, IntegerReverse[#]}] && ! PalindromeQ[#] && First[(d = IntegerDigits[#])] < Last[d] && PalindromeQ[Most@ Rest@ IntegerDigits[#]] &] (* Amiram Eldar, Oct 16 2021 *)

isok(p) = my(dp=digits(p), dr=Vecrev(dp), r=fromdigits(dr)); if (isprime(r) && (r>p) && isprime(p), sum(i=2, #dp-1, dp[i]==dr[i]) == #dp-2); \\ Michel Marcus, Oct 16 2021

Missing 179 added by Zak Seidov, Oct 15 2021

cp's OEIS Frontend

A263242 Larger of emirp pairs that are merely reversals of their end digits.

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