|
| |
|
|
A089653
|
|
(Product of prime factors of n) - 1 is a perfect square.
|
|
3
| |
|
|
2, 4, 5, 8, 10, 16, 17, 20, 25, 26, 32, 37, 40, 50, 52, 64, 65, 80, 82, 100, 101, 104, 122, 125, 128, 145, 160, 164, 170, 197, 200, 208, 226, 244, 250, 256, 257, 289, 290, 320, 325, 328, 338, 340, 362, 400, 401, 416, 442, 452, 485, 488, 500, 512, 530, 577, 580
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,1
|
|
|
EXAMPLE
| The prime factors of 10 are 2 and 5 and 2 * 5 - 1 = 9 is a square; so 10 belongs to the sequence.
|
|
|
MATHEMATICA
| ppf[n_] := Apply[Times, Transpose[FactorInteger[n]][[1]]]; Select[Range[2, 10^3], IntegerQ[Sqrt[ppf[ # ] - 1]] &]
|
|
|
CROSSREFS
| Cf. A089632. A091419 gives squares, A091420 gives square roots.
Sequence in context: A199799 A032937 A126684 * A180252 A191203 A114652
Adjacent sequences: A089650 A089651 A089652 * A089654 A089655 A089656
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jan 04 2004
|
| |
|
|
