|
| |
|
|
A138479
|
|
a(n) = smallest prime p such that 2n + p^2 is another prime, or 0 if no such prime exists.
|
|
10
| |
|
|
3, 3, 5, 3, 3, 5, 3, 5, 5, 3, 3, 7, 0, 3, 7, 3, 3, 5, 3, 7, 5, 3, 5, 5, 3, 3, 5, 0, 3, 7, 3, 3, 29, 0, 3, 5, 3, 5, 5, 3, 5, 5, 0, 3, 7, 3, 3, 19, 3, 3, 5, 3, 5, 7, 0, 5, 5, 0, 3, 11, 3, 5, 5, 3, 3, 5, 0, 11, 5, 3, 3, 7, 0, 3, 7, 0, 3, 5, 3, 11, 7, 3, 5, 5, 3, 3, 5, 0, 7, 7, 3, 3, 5, 3, 3, 7, 0, 11, 5, 0
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,1
|
|
|
COMMENTS
| For numbers n such that a(n) = 0 see A138685..
|
|
|
LINKS
| Eric Weisstein's World of Mathematics, Near-Square Prime
|
|
|
EXAMPLE
| 11=2+3^2 hence a(1)=3
13=4+3^2 hence a(2)=3
31=6+5^2 hence a(3)=5
17=8+3^2 hence a(4)=3
19=10+3^2 hence a(5)=3
37=12+5^2 hence a(6)=5
23=14+3^2 hence a(7)=3
41=16+5^2 hence a(8)=5
43=18+5^2 henec a(9)=5
29=20+3^2 hence a(10)=3
31=22+3^2 hence a(11)=3
73=24+7^2 hence a(12)=7
|
|
|
MATHEMATICA
| a = {}; Do[ p = 0; While[ (! PrimeQ[ 2*n + Prime[ p + 1 ]2 ]) && (p < 1000), p++ ]; If[ p < 1000, AppendTo[ a, Prime[ p + 1 ] ], AppendTo[ a, 0 ] ], {n, 1, 150} ]; a (*Artur Jasinski, Mar 26 2008*)
a[n_]:=If[Mod[n, 3]!=1, (For[m=1, !PrimeQ[2n+Prime[m]^2], m++ ]; Prime[m]), If[ !PrimeQ[2n+9], 0, 3]]; Table[a[n], {n, 100}] - Farideh Firoozbakht (mymontain(AT)yahoo.com), Mar 28 2008
|
|
|
CROSSREFS
| Cf. A002373, A020481, A049613, A059324 (?).
Sequence in context: A204903 A054906 A020483 * A202106 A136019 A063714
Adjacent sequences: A138476 A138477 A138478 * A138480 A138481 A138482
|
|
|
KEYWORD
| nonn,hard
|
|
|
AUTHOR
| Philippe LALLOUET (philip.lallouet(AT)orange.fr), Mar 20 2008
|
|
|
EXTENSIONS
| More terms from Artur Jasinski (grafix(AT)csl.pl) and Farideh Firoozbakht (mymontain(AT)yahoo.com), Mar 26 2008
|
| |
|
|
