

A164620


Primes p such that 1 +p*floor(p/2) is also prime.


4



2, 5, 13, 17, 41, 61, 89, 97, 101, 113, 149, 173, 229, 241, 281, 317, 349, 353, 373, 397, 409, 421, 433, 461, 509, 521, 661, 673, 761, 853, 881, 937, 941, 1013, 1093, 1109, 1249, 1289, 1297, 1373, 1433, 1549, 1741, 1753, 1913, 2113, 2213, 2269, 2281, 2297
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,1


LINKS



EXAMPLE

p=2 qualifies since 2*1+1=3 is prime. p=5 qualifies since 5*2+1=11 is prime.


MATHEMATICA

lst={}; Do[p=Prime[n]; If[PrimeQ[p*Floor[p/2]+1], AppendTo[lst, p]], {n, 3*6!}]; lst
Select[Prime[Range[350]], PrimeQ[1+#*Floor[#/2]]&] (* Harvey P. Dale, Apr 07 2015 *)


CROSSREFS



KEYWORD

nonn,easy


AUTHOR



EXTENSIONS



STATUS

approved



