|
%I #14 May 21 2018 02:28:13
%S 1,1,1,11,1,1221,1,1111,333,122221,1,11222211,1,12222221,1233321,
%T 11111111,1,111222222111,1,112222222211,123333321,1344444444431,1,
%U 1111222222221111,11111,12222222222221,333333333,1122222222222211,1,1011121222222221211101,1,1111111111111111,1233333333321
%N Algebraic cofactor of n-th repunit A002275(n).
%H Samuel Yates, <a href="http://www.geocities.jp/ma85003/math/repdigit.pdf">Cofactors of repunits</a>, Journal of Recreational Mathematics, Vol. 8(2), pp. 99, 1975-76.
%H Samuel Yates, <a href="http://www.jstor.org/stable/2689643">The Mystique of Repunits</a>, Math. Mag. 51 (1978), 22-28.
%F Equals A002275(n)/(product of terms in n-th row of A204846).
%o (PARI) lista(nn) = {vf = []; vfs = []; for (n=1, nn, if (n==1, print1(n, ", "), rn = (10^n-1)/9; f = factor(rn)[, 1]; vkeep = []; for (k = 1, #f~, if (!vecsearch(vfs, f[k]), vkeep = concat(vkeep, f[k])); ); print1(rn/prod(j=1, #vkeep, vkeep[j]), ", "); vf = concat(vf, vkeep); vfs = Set(vf); ); ); } \\ _Michel Marcus_, May 20 2018
%Y Cf. A002275, A102380, A204845, A204846, A204847.
%K nonn
%O 1,4
%A _N. J. A. Sloane_, Jan 19 2012
%E More terms from _Michel Marcus_, May 20 2018
|
