A134037 Concatenated first and last digits of Mersenne prime reversals.

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

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