A204848 Algebraic cofactor of n-th repunit A002275(n).

1, 1, 1, 11, 1, 1221, 1, 1111, 333, 122221, 1, 11222211, 1, 12222221, 1233321, 11111111, 1, 111222222111, 1, 112222222211, 123333321, 1344444444431, 1, 1111222222221111, 11111, 12222222222221, 333333333, 1122222222222211, 1, 1011121222222221211101, 1, 1111111111111111, 1233333333321

Offset: 1

Author

N. J. A. Sloane, Jan 19 2012

Keywords

• nonn

Links

• Samuel Yates, Cofactors of repunits, Journal of Recreational Mathematics, Vol. 8(2), pp. 99, 1975-76.
• Samuel Yates, The Mystique of Repunits, Math. Mag. 51 (1978), 22-28.

Crossrefs

Cf. A002275, A102380, A204845, A204846, A204847.

Programs

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

Formula

Equals A002275(n)/(product of terms in n-th row of A204846).

Extensions

More terms from Michel Marcus, May 20 2018