|
|
A356742
|
|
Numbers k such that k and k+2 both have exactly 4 divisors.
|
|
4
|
|
|
6, 8, 33, 55, 85, 91, 93, 123, 141, 143, 159, 183, 185, 201, 203, 213, 215, 217, 219, 235, 247, 265, 299, 301, 303, 319, 321, 327, 339, 341, 391, 393, 411, 413, 415, 445, 451, 469, 471, 515, 517, 533, 535, 543, 551, 579, 581, 589, 633, 667, 669, 679, 685, 687, 695, 697
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
6 and 8 are the only even terms: one of the two consecutive even numbers is divisible by 4, and the only multiple of 4 with exactly 4 divisors is 8.
|
|
LINKS
|
|
|
EXAMPLE
|
341 is a term since 341 and 343 both have 4 divisors.
|
|
MATHEMATICA
|
SequencePosition[DivisorSigma[0, Range[700]], {4, _, 4}][[All, 1]] (* Harvey P. Dale, Oct 07 2022 *)
|
|
PROG
|
(PARI) isA356742(n) = numdiv(n)==4 && numdiv(n+2)==4
|
|
CROSSREFS
|
Numbers k such that k and k+2 both have exactly m divisors: A001359 (m=2), this sequence (m=4), A356743 (m=6), A356744 (m=8).
Cf. also A039832 (numbers k such that k and k+1 both have exactly 4 divisors).
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|