|
|
A186621
|
|
Semiprimes - 1.
|
|
3
|
|
|
3, 5, 8, 9, 13, 14, 20, 21, 24, 25, 32, 33, 34, 37, 38, 45, 48, 50, 54, 56, 57, 61, 64, 68, 73, 76, 81, 84, 85, 86, 90, 92, 93, 94, 105, 110, 114, 117, 118, 120, 121, 122, 128, 132, 133, 140, 141, 142, 144, 145, 154, 157, 158, 160, 165, 168, 176, 177, 182, 184, 186, 193
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
Numbers of the form k-1 where k is semiprime (or biprime), namely a product of exactly two (not necessarily distinct) primes. Used as relative base sequence for analogies to sequences involving number of form (p-1) for prime p.
|
|
LINKS
|
|
|
FORMULA
|
|
|
EXAMPLE
|
The smallest semiprime is 4 = 2*2, so a(1) = 4-1 = 3.
|
|
MATHEMATICA
|
Select[Range[5000], 2 == Total[Transpose[FactorInteger[# + 1]][[2]]] &]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|