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#2: Post edited by user avatar trichoplax‭ · 2025-03-27T03:17:53Z (6 days ago)
Make wording more explicit
  • The number $4294967295$ has prime factors $3,5,17,257,\text{and }65537$.
  • The number is one less than a power of $2$, and its prime factors are all one more than a power of $2$. This made me wonder if this happens for other numbers that are one less than a power of $2$.
  • $N$ | $2^{N}-1$ | $\text{Prime factors}$
  • --- | --- | ---
  • $1$ | $1$ | $-$
  • $\boldsymbol{2}$ | $\boldsymbol{3}$ | $\boldsymbol{3}$
  • $3$ | $7$ | $7$
  • $\boldsymbol{4}$ | $\boldsymbol{15}$ | $\boldsymbol{3,5}$
  • $5$ | $31$ | $31$
  • $6$ | $63$ | $3,3,7$
  • $7$ | $127$ | $127$
  • $\boldsymbol{8}$ | $\boldsymbol{255}$ | $\boldsymbol{3,5,17}$
  • $9$ | $511$ | $7,73$
  • $10$ | $1023$ | $3,11,31$
  • $11$ | $2047$ | $23,89$
  • $12$ | $4095$ | $3,3,5,7,13$
  • $13$ | $8191$ | $8191$
  • $14$ | $16383$ | $3,43,127$
  • $15$ | $32767$ | $7,31,151$
  • $\boldsymbol{16}$ | $\boldsymbol{65535}$ | $\boldsymbol{3,5,17,257}$
  • It appears that each $N$ that is a power of $2$ gives a $2^N-1$ that has prime factors in a pattern. This pattern continues with the number I first mentioned:
  • $N$ | $2^{N}-1$ | $\text{Prime factors}$
  • --- | --- | ---
  • $2$ | $3$ | $3$
  • $4$ | $15$ | $3,5$
  • $8$ | $255$ | $3,5,17$
  • $16$ | $65535$ | $3,5,17,257$
  • $32$ | $4294967295$ | $3,5,17,257,65537$
  • Does this pattern continue indefinitely?
  • The number $4294967295$ has prime factors $3,5,17,257,\text{and }65537$.
  • The number is one less than a power of $2$, and its prime factors are all one more than a power of $2$. This made me wonder if this happens for other numbers that are one less than a power of $2$.
  • $N$ | $2^{N}-1$ | $\text{Prime factors}$
  • --- | --- | ---
  • $1$ | $1$ | $-$
  • $\boldsymbol{2}$ | $\boldsymbol{3}$ | $\boldsymbol{3}$
  • $3$ | $7$ | $7$
  • $\boldsymbol{4}$ | $\boldsymbol{15}$ | $\boldsymbol{3,5}$
  • $5$ | $31$ | $31$
  • $6$ | $63$ | $3,3,7$
  • $7$ | $127$ | $127$
  • $\boldsymbol{8}$ | $\boldsymbol{255}$ | $\boldsymbol{3,5,17}$
  • $9$ | $511$ | $7,73$
  • $10$ | $1023$ | $3,11,31$
  • $11$ | $2047$ | $23,89$
  • $12$ | $4095$ | $3,3,5,7,13$
  • $13$ | $8191$ | $8191$
  • $14$ | $16383$ | $3,43,127$
  • $15$ | $32767$ | $7,31,151$
  • $\boldsymbol{16}$ | $\boldsymbol{65535}$ | $\boldsymbol{3,5,17,257}$
  • It appears that each $N$ that is a power of $2$ gives a $2^N-1$ that has prime factors in a pattern of numbers one more than a power of $2$. This pattern continues with the number I first mentioned:
  • $N$ | $2^{N}-1$ | $\text{Prime factors}$
  • --- | --- | ---
  • $2$ | $3$ | $3$
  • $4$ | $15$ | $3,5$
  • $8$ | $255$ | $3,5,17$
  • $16$ | $65535$ | $3,5,17,257$
  • $32$ | $4294967295$ | $3,5,17,257,65537$
  • Does this pattern continue indefinitely?
#1: Initial revision by user avatar trichoplax‭ · 2025-03-25T23:19:26Z (7 days ago)
Prime factor pattern in numbers one less than a power of 2
The number $4294967295$ has prime factors $3,5,17,257,\text{and }65537$.

The number is one less than a power of $2$, and its prime factors are all one more than a power of $2$. This made me wonder if this happens for other numbers that are one less than a power of $2$.

$N$ | $2^{N}-1$ | $\text{Prime factors}$
--- | --- | ---
$1$ | $1$ | $-$
$\boldsymbol{2}$ | $\boldsymbol{3}$ | $\boldsymbol{3}$
$3$ | $7$ | $7$
$\boldsymbol{4}$ | $\boldsymbol{15}$ | $\boldsymbol{3,5}$
$5$ | $31$ | $31$
$6$ | $63$ | $3,3,7$
$7$ | $127$ | $127$
$\boldsymbol{8}$ | $\boldsymbol{255}$ | $\boldsymbol{3,5,17}$
$9$ | $511$ | $7,73$
$10$ | $1023$ | $3,11,31$
$11$ | $2047$ | $23,89$
$12$ | $4095$ | $3,3,5,7,13$
$13$ | $8191$ | $8191$
$14$ | $16383$ | $3,43,127$
$15$ | $32767$ | $7,31,151$
$\boldsymbol{16}$ | $\boldsymbol{65535}$ | $\boldsymbol{3,5,17,257}$

It appears that each $N$ that is a power of $2$ gives a $2^N-1$ that has prime factors in a pattern. This pattern continues with the number I first mentioned:

$N$ | $2^{N}-1$ | $\text{Prime factors}$
--- | --- | ---
$2$ | $3$ | $3$
$4$ | $15$ | $3,5$
$8$ | $255$ | $3,5,17$
$16$ | $65535$ | $3,5,17,257$
$32$ | $4294967295$ | $3,5,17,257,65537$

Does this pattern continue indefinitely?