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A283454 The square root of the smallest square referenced in A249025 (Numbers k such that 3^k - 1 is not squarefree). 3
2, 2, 11, 2, 2, 2, 2, 2, 11, 2, 2, 2, 2, 2, 11, 2, 2, 2, 2, 2, 11, 2, 2, 13, 2, 2, 2, 11, 2, 2, 2, 2, 2, 11, 2, 2, 2, 2, 2, 11, 2, 2, 2, 2, 2, 11, 2, 2, 2, 2, 2, 11, 2, 2, 2, 2, 2, 11, 2, 2, 2, 2, 2, 11, 2, 2, 2, 2, 2, 11, 2, 13, 2, 2, 2, 2, 11, 2, 2, 2, 2, 2, 11 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The terms are the smallest prime whose square divides 3^k-1, when it is not squarefree.

LINKS

Michel Marcus, Table of n, a(n) for n = 1..121

EXAMPLE

A249025(3)=5, 3^5-1 = 242 = 2*11*11. 242 is not squarefree the square being 11*11 = 121, the root being 11.

PROG

(PARI) lista(nn) = {for (n=1, nn, if (!issquarefree(k = 3^n-1), f = factor(k/core(k)); vsq = select(x->((x%2) == 0), f[, 2], 1); print1(f[vsq[1], 1], ", "); ); ); } \\ Michel Marcus, Mar 11 2017

CROSSREFS

Cf. A046027, A249025, A249739, A283453.

Sequence in context: A081088 A236369 A001038 * A027623 A037234 A141651

Adjacent sequences:  A283451 A283452 A283453 * A283455 A283456 A283457

KEYWORD

nonn

AUTHOR

Robert Price, Mar 07 2017

EXTENSIONS

More terms from Michel Marcus, Mar 11 2017

STATUS

approved

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Last modified September 27 19:04 EDT 2020. Contains 337388 sequences. (Running on oeis4.)