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 A134037 Concatenated first and last digits of Mersenne prime reversals. 3
 33, 77, 13, 71, 18, 11, 75, 72, 12, 16, 71, 71, 16, 75, 71, 71, 14, 12, 11, 72, 14, 13, 12, 14, 14, 14, 18, 75, 75, 15, 77, 71, 11, 74, 18, 16, 11, 14, 19, 71, 72, 71, 13, 11, 72, 11, 13 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Not all reversals of Mersenne primes are primes. Concatenation is a convenient way to see whether the prime reversal might be prime (obviously not if ending in an even number or 5). LINKS Table of n, a(n) for n=1..47. Carlos Rivera, Puzzle 417. M(e) reversed primes, The Prime Puzzles & Problems Connection. FORMULA Generate the Mersenne prime sequence. Reverse the primes. Find the value of the first and last digits and concatenate. EXAMPLE a(4)=71 because the first and last digits of the 4th Mersenne prime 127 are 1 and 7. Reversed they are 7 and 1 and concatenated for convenience, 71. MATHEMATICA f[n_] := FromDigits[Part[IntegerDigits[n], {-1, 1}]]; f /@ (2^ MersennePrimeExponent[Range[47]] - 1) (* Amiram Eldar, Feb 16 2020 *) CROSSREFS Cf. A134038 A134039. Sequence in context: A049012 A137187 A354916 * A138841 A248979 A246409 Adjacent sequences: A134034 A134035 A134036 * A134038 A134039 A134040 KEYWORD nonn,base,more AUTHOR Enoch Haga, Oct 02 2007 EXTENSIONS a(21)-a(47) from Amiram Eldar, Feb 16 2020 STATUS approved

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Last modified August 11 23:45 EDT 2024. Contains 375082 sequences. (Running on oeis4.)