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A283453 The smallest square referenced in A249025 (Numbers k such that 3^k - 1 is not squarefree). 2
4, 4, 121, 4, 4, 4, 4, 4, 121, 4, 4, 4, 4, 4, 121, 4, 4, 4, 4, 4, 121, 4, 4, 169, 4, 4, 4, 121, 4, 4, 4, 4, 4, 121, 4, 4, 4, 4, 4, 121, 4, 4, 4, 4, 4, 121, 4, 4, 4, 4, 4, 121, 4, 4, 4, 4, 4, 121, 4, 4, 4, 4, 4, 121, 4, 4, 4, 4, 4, 121, 4, 169, 4, 4, 4, 4, 121 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
a(n) = A283454(n)^2. - Amiram Eldar, Feb 12 2021
EXAMPLE
A249025(3)=5, 3^5-1 = 242 = 2*11*11. 242 is not squarefree the square being 11*11 = 121.
MATHEMATICA
psq[n_] := If[(f = Select[FactorInteger[n], Last[#] > 1 &]) == {}, 1, f[[1, 1]]^2]; psq /@ Select[3^Range[100] - 1, !SquareFreeQ[#] &] (* Amiram Eldar, Feb 12 2021 *)
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]^2, ", "); ); ); } \\ Michel Marcus, Mar 11 2017
CROSSREFS
Sequence in context: A009559 A163196 A219453 * A055071 A213142 A357540
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 March 28 09:04 EDT 2024. Contains 371240 sequences. (Running on oeis4.)