

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
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OFFSET

1,1


COMMENTS

Center of the smallest 2ntuple 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.


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



