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 A055381 Smallest number such that n closest primes below and above it are symmetric. 6
 4, 9, 12, 30, 30, 165, 8021811, 1071065190, 1613902650, 1797595815015, 633925574060895, 22930603692243585 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Center of the smallest 2n-tuple of consecutive 2n odd primes with symmetrical gaps (cf. A055382). LINKS FORMULA a(n) = ( A055382(n) + A000040(A000720(A055382(n))+2n) ) / 2 = ( A055382(n) + A151800(...(A151800(A055382(n)))...) ) / 2, where A151800 is iterated 2n times. - Max Alekseyev, Jul 23 2015 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 Cf. A001223, A055380, A055382. Sequence in context: A283105 A179808 A083351 * A287498 A174911 A032820 Adjacent sequences:  A055378 A055379 A055380 * A055382 A055383 A055384 KEYWORD more,nonn 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 STATUS approved

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Last modified May 26 12:39 EDT 2020. Contains 334626 sequences. (Running on oeis4.)