

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
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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



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



KEYWORD

nonn,base,more


AUTHOR



EXTENSIONS



STATUS

approved



