Fermat tæl

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In rīmcræftum, Fermat tæl, genemnod æfter Pierre de Fermat, þǣm þe hīe ærest hogde, is positif tæl mid scape:

þider n is unnegatif tæl. Þā ærest eahta Fermat talu sind (æfterfylgung A000215 on OEIS):

F₀ = 2¹ + 1 = 3

F₁ = 2² + 1 = 5

F₂ = 2⁴ + 1 = 17

F₃ = 2⁸ + 1 = 257

F₄ = 2¹⁶ + 1 = 65537

F₅ = 2³² + 1 = 4294967297 = 641 × 6700417

F₆ = 2⁶⁴ + 1 = 18446744073709551617 = 274177 × 67280421310721

F₇ = 2¹²⁸ + 1 = 340282366920938463463374607431768211457 = 59649589127497217 × 5704689200685129054721

Gif 2ⁿ + 1 frumtæl is, man cynþ ācȳðan þæt n must bēon 2-miht. (Gif n = ab þæt 1 < a, b < n and b is ofertæl, man hæfþ 2ⁿ + 1 ≡ (2^a)^b + 1 ≡ (−1)^b + 1 ≡ 0 (mod 2^a + 1).)

For þǣm ǣlc frumtæl mid scape 2ⁿ + 1 is Fermat tæl, and þās frumtalu hātte Fermat frumtalu. Man wāt ǣnlīce fīf Fermat frumtalu: F₀, ... ,F₄.

Innungbred 1 Basic properties 2 See swelce eac 3 Ūtweardlican bendas: 4 References

[ādihtan] Basic properties

Þā Fermat talu āfylaþ þis recurrence relations

F_n = (F_{n - 1} - 1)² + 1

for n ≥ 2.

[ādihtan] See swelce eac

• Mersenne frumtæl
• Lucas's theorem
• Proth's theorem
• Pseudoprime
• Primality test
• Constructible tæl
• Sierpinski tæl

[ādihtan] Ūtweardlican bendas:

• Sequence of Fermat numbers
• Prime Glossary Page on (+d,āc) Fermat Numbers
• Generalized Fermat Prime gesecan
• History of Fermat Numbers
• Unification of Mersenne ge Fermat Numbers
• Prime Factors of Fermat Numbers

[ādihtan] References

• 17 Wordcræftas on Fermat talu: From Number Theory to Geometry, Michal Krizek, Florian Luca, Lawrence Somer, Springer, CMS Books 9, ISBN 0387953329 (Þis bóc hæfþ extensive list of references.)