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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: A240884 A049012 A137187 * 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 May 17 16:03 EDT 2021. Contains 343980 sequences. (Running on oeis4.)