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A204848 Algebraic cofactor of n-th repunit A002275(n). 3
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 (list; graph; refs; listen; history; text; internal format)
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 A010190

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

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Last modified April 21 23:52 EDT 2021. Contains 343156 sequences. (Running on oeis4.)