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

1,4

Links

Table of n, a(n) for n=1..33.

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.

Formula

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

Prog

(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

Crossrefs

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

Sequence in context: A286642 A290860 A284232 * A027645 A193925 A365644

Adjacent sequences: A204845 A204846 A204847 * A204849 A204850 A204851

Keyword

nonn

Author

N. J. A. Sloane, Jan 19 2012

Extensions

More terms from Michel Marcus, May 20 2018

Status

approved