|
Search: id:A113525
|
|
|
| A113525 |
|
Semiprimes in third spoke of a hexagonal spiral (A056107). |
|
+0
2
|
|
| 4, 49, 301, 589, 973, 2353, 2701, 3073, 4333, 5293, 5809, 6349, 6913, 7501, 8749, 9409, 10801, 11533, 13069, 14701, 15553, 16429, 23233, 24301, 25393, 27649, 30001
(list; graph; listen)
|
|
|
OFFSET
|
1,1
|
|
|
COMMENT
|
a(1) = 4 because A056107(1) = 3*1^2 + 1 = 4 = 2^2 is semiprime. A056107(2) = 3*2^2 + 1 = 13 is not in the sequence, as it is a prime. A056107(3) = 3*3^2 + 1 = 28 = 2^2 * 7 is not in the sequence, as it is a 3-almost prime. a(16) = 9409 because A056107(56) = 3*56^2 + 1 = 9409 = 97^2 is semiprime. a(27) = 30001 because A056107(100) = 3*100^2 + 1 = 30001 = 19 * 1579 is semiprime.
|
|
FORMULA
|
{a(n)} = {3*n^2 + 1 iff semiprime}. {a(n)} = A056107 INTERSECT A001358.
|
|
CROSSREFS
|
Cf. A001358, A056107.
Sequence in context: A100256 A163944 A000596 this_sequence A064751 A045787 A067474
Adjacent sequences: A113522 A113523 A113524 this_sequence A113526 A113527 A113528
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
Jonathan Vos Post (jvospost3(AT)gmail.com), Jan 12 2006
|
|
|
Search completed in 0.002 seconds
|
