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 A139260 #8 Aug 29 2018 16:48:22
%S A139260 5,57,577,5772,57721,577215,5772156,57721566,577215664,5772156649,
%T A139260 57721566490,577215664901,5772156649015,57721566490153,
%U A139260 577215664901532,5772156649015328,57721566490153286,577215664901532860
%N A139260 Decimal expansion of Euler's constant (or Euler-Mascheroni constant) gamma truncated to n places.
%H A139260 G. C. Greubel, <a href="/A139260/b139260.txt">Table of n, a(n) for n = 1..995</a>
%e A139260 n ... Successive digits of a(n)
%e A139260 1 ............ ( 5 )
%e A139260 2 ......... . ( 5 7 )
%e A139260 3 .......... ( 5 7 7 )
%e A139260 4 ......... ( 5 7 7 2 )
%e A139260 5 ........ ( 5 7 7 2 1 )
%e A139260 6 ....... ( 5 7 7 2 1 5 )
%e A139260 7 ...... ( 5 7 7 2 1 5 6 )
%e A139260 8 ..... ( 5 7 7 2 1 5 6 6 )
%e A139260 9 .... ( 5 7 7 2 1 5 6 6 4 )
%e A139260 10 .. ( 5 7 7 2 1 5 6 6 4 9 )
%t A139260 With[{em=RealDigits[EulerGamma,10,20][[1]]},Table[FromDigits[Take[ em,n]], {n,20}]] (* _Harvey P. Dale_, Nov 22 2011 *)
%Y A139260 Decimal expansion of gamma: A001620. Cf. A011543, A011545 A011551, A139258, A139259, A139261.
%K A139260 easy,nonn,base
%O A139260 1,1
%A A139260 _Omar E. Pol_, May 01 2008