|
Search: id:A115411
|
|
|
| A115411 |
|
a(n) = least k such that semiprime(n) divides k-th triangular number. |
|
+0
1
|
|
| 7, 3, 8, 4, 7, 5, 6, 11, 24, 12, 11, 16, 14, 19, 12, 23, 48, 17, 10, 18, 28, 31, 25, 23, 36, 21, 40, 34, 43, 29, 13, 30, 47, 19, 52, 36, 45, 59, 34, 120, 60, 41, 42, 56, 67, 47, 71, 65, 29, 72, 30, 79, 53, 69, 83, 168, 59, 88, 60, 74, 33, 96, 66, 100, 28, 40, 103, 76, 71, 107, 85
(list; graph; listen)
|
|
|
OFFSET
|
1,1
|
|
|
COMMENT
|
a(n) = MIN[k such that A001358(n) | A000217(k)].
|
|
EXAMPLE
|
a(1) = 7 because SP(1) = semiprime(1) = 4, Triangular number T(7) = 7*(7+1)/2 = 28 and 7 divides 28.
a(2) = 3 because SP(2) = 6 | T(3) = 6.
a(3) = 8 because SP(3) = 9 | T(8) = 36.
a(9) = 24 because SP(9) = 25 | T(24) = 300.
a(17) = 48 because SP(17) = 49 | T(48) = 1176.
|
|
MATHEMATICA
|
a = Select[Range@215, Plus @@ Last /@ FactorInteger@# == 2 &]; f[n_] := Block[{k = 1}, While[ Mod[k(k + 1)/2, a[[n]]] > 0, k++ ]; k]; Array[f, 71] (* Robert G. Wilson v *)
|
|
CROSSREFS
|
Cf. A000217, A001358.
Sequence in context: A160578 A166201 A111197 this_sequence A019726 A011330 A093587
Adjacent sequences: A115408 A115409 A115410 this_sequence A115412 A115413 A115414
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
Jonathan Vos Post (jvospost3(AT)gmail.com), Mar 08 2006
|
|
EXTENSIONS
|
More terms from Robert G. Wilson v (rgwv(at)rgwv.com), May 01 2006
|
|
|
Search completed in 0.002 seconds
|
