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A119751 a(1) = 1; a(n) = first odd number greater than a(n-1) such that a(n) + a(i) + 1 is prime for all i=1,2,...,n. 9
1, 3, 9, 69, 429, 4089, 86529, 513099, 913569, 7914339, 6593621379, 9366241599, 456246278469, 4565283812559 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
FORMULA
2*a(n)+1 = A113875(n). - Don Reble, Aug 17 2021
MATHEMATICA
Table[If[n == 1, a[1] = 1, j = a[n - 1] + 2; While[a[n] = j; !
AllTrue[Table[a[i] + a[n] + 1, {i, 1, n}], PrimeQ], j += 2]; j]
, {n, 1, 7}] (* Robert Price, Apr 03 2019 *)
PROG
(PARI) isok(va, k, n) = if (isprime(2*k+1), for (i=1, n-1, if (! isprime(va[i]+k+1), return(0))); return(1));
lista(nn) = my(va=vector(nn)); va[1]=1; for (n=2, nn, my(k=va[n-1]+2); while (!isok(va, k, n), k+=2); va[n] = k); va; \\ Michel Marcus, Mar 07 2023
CROSSREFS
Sequence in context: A093351 A018543 A026090 * A276475 A084543 A318030
KEYWORD
nonn,hard,more
AUTHOR
Walter Kehowski, Jun 17 2006
EXTENSIONS
a(13)-a(14) from Donovan Johnson, Mar 23 2008
Corrected and edited by Walter Kehowski, Oct 18 2008
STATUS
approved

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Last modified February 21 20:41 EST 2024. Contains 370237 sequences. (Running on oeis4.)