

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



