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A055382 Smallest prime starting a sequence of 2n consecutive odd primes with symmetrical gaps about the center. 14
3, 5, 5, 17, 13, 137, 8021749, 1071065111, 1613902553, 1797595814863, 633925574060671, 22930603692243271 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
a(13) <= 5179852391836338871. The solution was found by the BOINC project "SPT test project". - Natalia Makarova, Dec 06 2023
LINKS
Discussion at the scientific forum dxdy.ru, Distributed computing project (in Russian)
Symmetric Prime Tuples, SPT test project
FORMULA
For n>1, a(n) = A081235(n) = A175309(2n-1).
EXAMPLE
The first term is 3 since the 2 primes 3, 5 have a gap of 2, which is trivially symmetric about its center.
The second term is 5 since the 4 primes 5, 7, 11, 13 have gaps 2, 4, 2, which is symmetric about its center.
The twelve primes 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193 have gaps 2, 10, 2, 6, 6, 4, 6, 6, 2, 10, 2 - symmetric about the middle, so a(6) = 137.
MATHEMATICA
Table[i = 1;
While[x = Differences[Table[Prime[k + i], {k, 2 n}]];
x != Reverse[x], i++]; Prime[i + 1], {n, 6}] (* Robert Price, Oct 12 2019 *)
CROSSREFS
See A081235 for another version.
Sequence in context: A318351 A137780 A079372 * A165235 A370553 A200771
KEYWORD
more,nonn
AUTHOR
Jud McCranie, Jun 23 2000
EXTENSIONS
a(10) from Donovan Johnson, Mar 09 2008
Minor edits by N. J. A. Sloane, Apr 02 2010
a(11) from Dmitry Petukhov, added by Max Alekseyev, Aug 08 2014
a(12) from an anonymous participant of the project, added by Max Alekseyev, Jul 21 2015
STATUS
approved

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Last modified July 23 12:38 EDT 2024. Contains 374549 sequences. (Running on oeis4.)