|
| |
|
|
A058383
|
|
Primes of form 1+(2^a)*(3^b), a>0, b>0.
|
|
13
| |
|
|
7, 13, 19, 37, 73, 97, 109, 163, 193, 433, 487, 577, 769, 1153, 1297, 1459, 2593, 2917, 3457, 3889, 10369, 12289, 17497, 18433, 39367, 52489, 139969, 147457, 209953, 331777, 472393, 629857, 746497, 786433, 839809, 995329, 1179649, 1492993
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,1
|
|
|
COMMENTS
| Prime numbers n such that cos(2pi/n) is an algebraic number of a 3-smooth degree, but not a 2-smooth degree. - Artur Jasinski (grafix(AT)csl.pl), Dec 13 2006
Contribution from Antonio M. Oller-Marc\'en (oller(AT)unizar.es), Sep 24 2009: (Start)
In this case g.c.d.(a,b) is a power of 2.
A regular polygon of n sides is constructible by paper folding if and only if n=2^r3^sp_1...p_t with p_i being distinct primes of this kind. (End)
|
|
|
LINKS
| T. D. Noe, Table of n, a(n) for n = 1..1000
|
|
|
FORMULA
| 1+A033845(n) is prime
|
|
|
MATHEMATICA
| Do[If[Take[FactorInteger[EulerPhi[2n + 1]][[ -1]], 1] == {3} && PrimeQ[2n + 1], Print[2n + 1]], {n, 1, 10000}] - Artur Jasinski (grafix(AT)csl.pl), Dec 13 2006
nn=10^10; Sort[Reap[Do[n=2^i 3^j; If[n<=nn && PrimeQ[n+1], Sow[n+1]], {i, Log[2, nn]}, {j, Log[3, nn]}]][[2, 1]]]
|
|
|
CROSSREFS
| Cf. A033845, A000423, A125866.
Sequence in context: A040034 A176229 A110074 * A005471 A040096 A073648
Adjacent sequences: A058380 A058381 A058382 * A058384 A058385 A058386
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Dec 20 2000
|
| |
|
|
