login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A177516 Odd numbers m = p*q such that p and q are distinct primes and (p-1) divides (q-1). 4
15, 21, 33, 39, 51, 57, 65, 69, 85, 87, 91, 93, 111, 123, 129, 133, 141, 145, 159, 177, 183, 185, 201, 205, 213, 217, 219, 237, 249, 259, 265, 267, 291, 301, 303, 305, 309, 321, 327, 339, 341, 365, 381, 393, 411, 417, 427, 445, 447, 451, 453, 469, 471, 481 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Neither p nor q can equal 2, i.e., 2 is not a permissible prime here. - Harvey P. Dale, May 04 2011
LINKS
EXAMPLE
(3 - 1) divides (5 - 1), so 3 * 5 = 15 is in this sequence.
(5 - 1) divides (17 - 1) so 5 * 17 = 85 is in this sequence.
(5 - 1) does not divide (19 - 1), so 5 * 19 = 95 is not in this sequence.
MATHEMATICA
Table[If[i < j && IntegerQ[(Prime[j] - 1)/(Prime[i] - 1)], Prime[j] * Prime[i]], {i, 2, 100}, {j, 2, 100}] // Flatten // Union
Union[Times@@@Select[Subsets[Prime[Range[2, 100]], {2}], Divisible[Last[#] - 1, First[#] - 1] &]] (* Harvey P. Dale, May 04 2011 *)
CROSSREFS
Cf. A046388.
Sequence in context: A198680 A300117 A214044 * A127329 A043326 A179996
KEYWORD
nonn
AUTHOR
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 12:26 EDT 2024. Contains 371254 sequences. (Running on oeis4.)