|
|
A057654
|
|
Numbers n such that sigma(n)^2 - phi(n)^2 is a perfect square.
|
|
1
|
|
|
1, 95, 99, 146, 323, 377, 1095, 1102, 1351, 1368, 1630, 1919, 1943, 2261, 2639, 2743, 3915, 4607, 4743, 5042, 5045, 5183, 5249, 6347, 6497, 7389, 8265, 8307, 8749, 9407, 9701, 10877, 12535, 13184, 13253, 14344, 14535, 16965, 18405, 19493, 19836
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
LINKS
|
|
|
EXAMPLE
|
sigma(95)^2 - phi(95)^2 = 120^2 - 72^2 = 96^2, so 95 is a term of the sequence.
|
|
MATHEMATICA
|
Select[Range[10^4], IntegerQ[Sqrt[DivisorSigma[1, # ]^2 - EulerPhi[ # ]^2]] &]
|
|
CROSSREFS
|
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|