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 A224793 Least prime p which generates exactly n primes of the form p+q-1 where q < p is prime, or 0 if (conjecturally) no such p exists. 0
 2, 5, 11, 13, 47, 41, 31, 107, 43, 73, 131, 61, 191, 97, 293, 139, 353, 127, 163, 151, 0, 229, 283, 223, 659, 181, 929, 313, 241, 211, 367, 701, 271, 397, 379, 457, 337, 1031, 1259, 607, 331, 463, 643, 613, 1409, 733, 911, 1091, 541, 1997, 421, 727, 709, 673 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(n) = 0 for n = 20, 165, 467, ... . Do there exist infinitely many such values of n? These values of 0 are all conjectural. - Robert Israel, Apr 28 2021 LINKS Table of n, a(n) for n=0..53. EXAMPLE a(1) = 5 since 5 is the least prime that generates exactly one prime 7=5+3-1 of the given form. Again a(3) = 13 since 13 generates exactly 3 primes 17=13+5-1, 19=13+7-1 and 23=13+11-1 of the given form. MATHEMATICA Cn[n_] := Module[{c}, p = Prime[n]; c = 0; i = 1; While[i < n, If[PrimeQ[p + Prime[i] - 1], c = c + 1] i++]; c]; t = {}; Do[p = 0; j = 0; While[++j < 2000 && p != 1, If[Cn[j] == k, AppendTo[t, Prime[j]]; p = 1, p = 0]]; If[p == 0, AppendTo[t, 0]], {k, 0, 200}]; t CROSSREFS Cf. A072669, A224748. Sequence in context: A106283 A020629 A355657 * A272852 A210506 A097055 Adjacent sequences: A224790 A224791 A224792 * A224794 A224795 A224796 KEYWORD nonn AUTHOR Jayanta Basu, Apr 18 2013 EXTENSIONS Definition clarified by Robert Israel, Apr 28 2021 STATUS approved

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Last modified June 5 05:23 EDT 2023. Contains 363130 sequences. (Running on oeis4.)