OFFSET
1,1
COMMENTS
3-term arithmetic progressions are ordered first by highest term, then by middle term, and last by lowest term.
Is there a proof that the sequence is infinite?
LINKS
FORMULA
EXAMPLE
The indices of 5,11,17 form the arithmetic progression of primes 3,5,7.
The indices of 461,617,773 form the arithmetic progression of primes 89,113,137.
MAPLE
l:= NULL: nn:= 2000: # nn = upper limit for index of largest prime found
for n from 3 to nn do
if isprime(n) then
for i from iquo(n-1, 2) to 1 by -1 do
if isprime(n-i) and isprime(n-2*i) then
p, q, r:= map(ithprime, [seq(n-i*j, j=0..2)])[];
if p-q = q-r then l:= l, r, q, p
fi fi od fi od: l; # Alois P. Heinz, Aug 12 2019
CROSSREFS
KEYWORD
nonn,look
AUTHOR
Jonathan Sondow, Aug 11 2019
EXTENSIONS
More terms from Alois P. Heinz, Aug 12 2019
STATUS
approved