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A055381 Smallest number such that n closest primes below and above it are symmetric. 5
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

Table of n, a(n) for n=1..12.

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.

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 January 23 02:32 EST 2019. Contains 319365 sequences. (Running on oeis4.)