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 A139259 #8 Jun 30 2025 10:49:07 %S A139259 5,5,5,5,7,5,5,7,7,5,5,7,7,7,5,5,7,7,7,7,5,5,7,7,2,7,7,5,5,7,7,2,2,7, %T A139259 7,5,5,7,7,2,1,2,7,7,5,5,7,7,2,1,1,2,7,7,5,5,7,7,2,1,5,1,2,7,7,5,5,7, %U A139259 7,2,1,5,5,1,2,7,7,5 %N A139259 Triangle read by rows: row n lists the digits of A139258(n), the palindromic number formed from the reflected decimal expansion of Euler's constant (or Euler-Mascheroni constant) gamma. %C A139259 Also, successive digits of A139258. %e A139259 Triangle begins: %e A139259 ....... 5 %e A139259 ...... 5,5 %e A139259 ..... 5,7,5 %e A139259 .... 5,7,7,5 %e A139259 ... 5,7,7,7,5 %t A139259 a[n_]:=FromDigits[Join[RealDigits[EulerGamma,10,Ceiling[n/2]][[1]],Reverse[RealDigits[EulerGamma,10,Floor[n/2]][[1]]]]];IntegerDigits/@Array[a,12]//Flatten (* _James C. McMahon_, Jun 29 2025 *) %Y A139259 Decimal expansion of gamma: A001620. %Y A139259 Cf. A138068, A138070, A138072, A139258, A139260, A139261. %K A139259 easy,nonn,tabl,base %O A139259 1,1 %A A139259 _Omar E. Pol_, May 01 2008