This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A028335 N0189 #68 Oct 16 2024 09:22:29 %S A028335 1,1,2,3,4,6,6,10,19,27,33,39,157,183,386,664,687,969,1281,1332,2917, %T A028335 2993,3376,6002,6533,6987,13395,25962,33265,39751,65050,227832,258716, %U A028335 378632,420921,895932,909526,2098960,4053946,6320430,7235733,7816230,9152052,9808358,11185272 %N A028335 Number of decimal digits in n-th Mersenne prime. %D A028335 Albert H. Beiler, Recreations in the Theory of Numbers, Dover, NY, 1964, p. 19. %D A028335 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). %H A028335 Amiram Eldar, <a href="/A028335/b028335.txt">Table of n, a(n) for n = 1..48</a> (terms 1..47 from Ivan Panchenko) %H A028335 Chris K. Caldwell, <a href="http://www.utm.edu/research/primes/mersenne/index.html">Mersenne Primes</a>. %H A028335 GIMPS, <a href="https://www.mersenne.org/primes/">List of Known Mersenne Prime Numbers</a>. %H A028335 Romeo Meštrović, <a href="http://arxiv.org/abs/1202.3670">Euclid's theorem on the infinitude of primes: a historical survey of its proofs (300 BC--2012) and another new proof</a>, arXiv preprint arXiv:1202.3670 [math.HO], 2012-2023. %F A028335 a(n) = floor(A000043(n)*log(2)/log(10)) + 1. %F A028335 a(n) = A055642(A000668(n)). - _Michel Marcus_, Apr 07 2018 %e A028335 A000668(6) = 2^17-1 = 131071 has 6 decimal digits, so a(6) = 6. %e A028335 A000668(10) = 2^89-1 = 618,970,019,642,690,137,449,562,111 has 27 digits, so a(10) = 27. %p A028335 seq(length(numtheory:-mersenne([i])),i=1..45); # _Robert Israel_, Feb 02 2018 %t A028335 IntegerLength[2^Array[MersennePrimeExponent, 45] - 1] (* _Jean-François Alcover_, Feb 17 2018 *) %t A028335 a[n_] := Floor[MersennePrimeExponent[n]/Log2[10]] + 1; Array[a, 48] (* _Amiram Eldar_, Oct 16 2024 *) %Y A028335 See A000043, which is the main entry for this sequence. %Y A028335 Cf. A000668, A055642. %K A028335 nonn,base %O A028335 1,3 %A A028335 _N. J. A. Sloane_ %E A028335 More terms from _Enoch Haga_, Dec 18 2001 %E A028335 a(38) from _Harry J. Smith_, Apr 17 2003 %E A028335 a(39) from _Omar E. Pol_, Oct 28 2007 %E A028335 a(40)-a(41) from _Jason Kimberley_, Jan 05 2012 %E A028335 a(42)-a(45) from _Patrick J. McNab_, Feb 01 2018