A217606 a(n) is the least unused prime greater than 3 such that (a(n) + a(n-1))/2 is prime, with a(0)=13.

13, 61, 73, 181, 37, 97, 109, 193, 229, 157, 241, 313, 349, 277, 337, 397, 421, 373, 541, 433, 409, 457, 757, 661, 577, 709, 613, 601, 853, 769, 733, 1021, 997, 877, 829, 673, 1033, 1009, 1069, 1117, 1129, 937, 1201, 1297, 1549, 1093, 1153, 1249, 1213, 1381

Offset: 0

Author

Pedja Terzic, Oct 08 2012

Keywords

• nonn

Comments

Conjecture: every prime of the form 12k+1 is a member.

Crossrefs

Cf. A086519.

Programs

Maple

a:=5:
l:=13:
L:=[l]:
while l < 3400 do
if isprime((l+a)/2) then
if not(a in L) then
if not a mod 12 = 1 then
print(a);
break;
end if;
L:=[op(L),a]:
l:=a:
a:=5:
else
a:=nextprime(a):
end if;
else
a:=nextprime(a):
end if;
end do;
L;