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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. 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

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

LINKS

Table of n, a(n) for n=0..49.

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;

CROSSREFS

Cf. A086519.

Sequence in context: A146764 A336794 A145474 * A002647 A306127 A118711

Adjacent sequences:  A217603 A217604 A217605 * A217607 A217608 A217609

KEYWORD

nonn

AUTHOR

Pedja Terzic, Oct 08 2012

STATUS

approved

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Last modified May 13 17:46 EDT 2021. Contains 343864 sequences. (Running on oeis4.)