|
|
A030513
|
|
Numbers with 4 divisors.
|
|
39
|
|
|
6, 8, 10, 14, 15, 21, 22, 26, 27, 33, 34, 35, 38, 39, 46, 51, 55, 57, 58, 62, 65, 69, 74, 77, 82, 85, 86, 87, 91, 93, 94, 95, 106, 111, 115, 118, 119, 122, 123, 125, 129, 133, 134, 141, 142, 143, 145, 146, 155, 158, 159, 161, 166, 177, 178, 183, 185, 187
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
Numbers which are either the product of two distinct primes (A006881) or the cube of a prime (A030078).
Since A119479(4)=3, there are never more than 3 consecutive integers in the sequence. Triples of consecutive integers start at 33, 85, 93, 141, 201, ... (A039833). No such triple contains a term of the form p^3. - Ivan Neretin, Feb 08 2016
Numbers that are equal to the product of their proper divisors (A007956) (proof in Sierpiński). - Bernard Schott, Apr 04 2022
|
|
REFERENCES
|
Wacław Sierpiński, Elementary Theory of Numbers, Ex. 2 p. 174, Warsaw, 1964.
|
|
LINKS
|
R. J. Mathar, Maple programs for A030638, A030637, A030636, A030635, A030634, A030633, A030632, A030631, A030630, A030629, A030628, A030627, A030626, A030516, A030515, A030514, A030513
|
|
FORMULA
|
|
|
MATHEMATICA
|
Select[Range[200], DivisorSigma[0, #]==4&] (* Harvey P. Dale, Apr 06 2011 *)
|
|
PROG
|
(Magma) [n: n in [1..200] | DivisorSigma(0, n) eq 4]; // Vincenzo Librandi, Jul 16 2015
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy,nice
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|