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A307818 Numbers k such that A240718(k) = 0. 0
1, 2, 3, 4, 5, 6, 9, 12, 15, 19, 49, 61, 63, 64, 110, 151, 154, 166, 173, 244, 278, 427, 454, 481, 496, 572, 575, 637, 677, 680, 681, 691, 704, 712, 766, 884, 928, 964, 1039, 1094, 1100, 1219, 1256, 1265, 1309, 1321, 1729, 1909, 1924, 2309, 2443, 2686, 2989, 3001, 3004, 3713, 4798, 4801, 5134, 5311, 5719, 5821, 6443, 6574, 6781, 7099, 7339, 8251, 9454, 10684, 11416, 11713, 11728, 21766, 27122, 31637 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
k is in the sequence if there are no primes p < sqrt(2*k-2) such that 2*k-p is prime.
There are no other terms < 10^7.
Conjecture: 31637 is the last term.
LINKS
EXAMPLE
a(7)=9 is in the sequence because the primes < sqrt(2*9-2)=4 are 2 and 3, and neither 2*9-2=16 nor 2*9-3=15 is prime.
MAPLE
P:= NULL: Res:= 1: nextp:= 2:
for n from 2 to 10^6 do
while nextp^2 < 2*n-2 do
P:= P, nextp;
nextp:= nextprime(nextp);
od;
if andmap(t -> not isprime(2*n-t), [P]) then
Res:= Res, n
fi;
od:
Res;
CROSSREFS
Cf. A240718.
Sequence in context: A008813 A133463 A187550 * A358033 A057492 A178715
KEYWORD
nonn
AUTHOR
Robert Israel, Apr 30 2019
STATUS
approved

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Last modified June 21 07:08 EDT 2024. Contains 373540 sequences. (Running on oeis4.)