A209385 Values of the first prefixing digits for Mersenne primes.

1, 1, 1, 4, 1, 10, 1, 36, 15, 58, 57, 55, 310, 177, 51, 2389, 973, 532, 1750, 63, 1032, 1240, 3757, 9994, 5854, 12870, 46147, 11923, 17113, 10296, 5977

Offset

1,4

Links

Table of n, a(n) for n=1..31.

Henri Lifchitz and Renaud Lifchitz, PRP Top Records

Example

For Mersenne 5, i.e., 8191, the first computed prefix is equal to 1 and gives 18191 which is also a prime, so a(5) = 1.

Mathematica

pfx[n_] := Module[{w = 10^(1+Floor[Log10[n]])}, k=n+w ; While[!PrimeQ[k], k+=w]; Floor[k/w]]; s={}; Do[m = 2^MersennePrimeExponent[n]-1; AppendTo[s, pfx[m]], {n, 1, 12}]; s (* Amiram Eldar, Nov 22 2018 based on Andrew Howroyd's pari code *)

Prog

(PARI)
pfx(n)={my(w=10^(1+logint(n, 10)), k=n+w); while(!ispseudoprime(k), k+=w); k\w}
{ for(n=1, 500, my(p=1<<prime(n)-1); if(ispseudoprime(p), print1(pfx(p), ", "))) } \\ Andrew Howroyd, Nov 17 2018

Crossrefs

Cf. A000668 (Mersenne primes), A202136.

Sequence in context: A059926 A306546 A138775 * A121529 A304429 A347115

Adjacent sequences: A209382 A209383 A209384 * A209386 A209387 A209388

Keyword

nonn,base,more

Author

Gilbert Mozzo, Mar 07 2012, Mar 18 2012

Status

approved