OFFSET
1,1
COMMENTS
Center of the smallest 2n-tuple of consecutive odd primes with symmetrical gaps (cf. A055382).
LINKS
Carlos Rivera, Problem 60. Symmetric primes on each side, The Prime Puzzles & Problems Connection.
FORMULA
EXAMPLE
The three primes on each side of 12 (13, 17, 19 and 11, 7, 5) are symmetrical with respect to the gaps, so a(3) = 12.
MATHEMATICA
Table[i = n + 2;
While[x =
Differences@
Flatten@{Table[NextPrime[i, k], {k, -n, -1}], i,
Table[NextPrime[i, k], {k, 1, n}]}; x != Reverse[x],
i++]; i, {n, 6}] (* Robert Price, Oct 12 2019 *)
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Jud McCranie, Jun 23 2000
EXTENSIONS
a(10) from Donovan Johnson, Mar 09 2008
a(11) from Dmitry Petukhov, added by Max Alekseyev, Aug 08 2014
a(12) computed from A055382(12) by Max Alekseyev, Jul 23 2015
Name clarified by Peter Munn, Jan 09 2023
STATUS
approved