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 A345421 #10 Jul 01 2021 23:41:04 %S A345421 1,1,-2,0,-3,2,5,-8,10,-4,9,16,6,-6,-20,-15,17,-26,-19,-10,21,34,12, %T A345421 -38,14,29,-44,46,-31,-16,-18,-56,-39,20,64,-43,45,70,24,-74,-51,26, %U A345421 82,-55,-28,57,-30,32,65,-98,100,-34,69,36,-110,-75,77,-116,-79,-40,81,42,44,89 %N A345421 Row 4 of array in A345417. %o A345421 (Python) %o A345421 from sympy.core.numbers import igcdex %o A345421 from sympy import prime %o A345421 def A345421(n): return igcdex(7, prime(n))[0] # _Chai Wah Wu_, Jul 01 2021 %Y A345421 Cf. A345417-A345422. %K A345421 sign %O A345421 1,3 %A A345421 _N. J. A. Sloane_, Jun 19 2021