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 A155751 #14 Jun 02 2025 01:19:12 %S A155751 1,-7,-2,-3,4,6,-8,5,-1,7,2,3,-4,-6,8,-5,1,-7,-2,-3,4,6,-8,5,-1,7,2,3, %T A155751 -4,-6,8,-5,1,-7,-2,-3,4,6,-8,5,-1,7,2,3,-4,-6,8,-5,1,-7,-2,-3,4,6,-8, %U A155751 5,-1,7,2,3,-4,-6,8,-5,1,-7,-2,-3,4,6,-8,5,-1,7,2,3,-4,-6,8,-5 %N A155751 A variation on 10^n mod 17. %C A155751 This is 10^n mod 17, using values -8,-7,...,7,8 (instead of 0..16). - _Don Reble_, Sep 02 2017. %C A155751 This sequence can be employed in a test for divisibility by 17 and works like A033940 works for 7. %C A155751 The use of negative coefficients ensures the termination of the test because the modulus of the intermediate sum at each step of the test decreases strictly. %C A155751 The test is successful if the final sum is 0. %C A155751 The negative coefficients have the form (10^n mod 17) - 17 when 10^n mod 17 > 8. %C A155751 Example: 9996 is divisible by 17 since |6*1 + 9*(-7) + 9*(-2) + 9*(-3)| = 102 and 2*1 + 0*(-7) + 1*(-2) = 0. %F A155751 a(n)= -a(n-8). G.f.:(1-7x-2x^2-3x^3+4x^4+6x^5-8x^6+5x^7)/(1+x^8). [From _R. J. Mathar_, Feb 13 2009] %Y A155751 Cf. A033940, A119910, A117378. %K A155751 easy,sign %O A155751 0,2 %A A155751 Ferruccio Guidi (fguidi(AT)cs.unibo.it), Jan 26 2009, Feb 08 2009