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 A231989 Least prime p such that f(0),...,f(n) are all primes, where f(0) = p, then f(i+1) = triangular(f(i))+1. 1
 3, 3, 43, 236367611, 31542795419 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Triangular(p) = p*(p+1)/2 (see A034953). LINKS EXAMPLE a(2) = 3 because 3 is the least prime such that the following are two primes: p1 = 3 * 4 / 2 + 1 = 7. p2 = 7 * 8 / 2 + 1 = 29. a(3) = 43 because 43 is the least prime such that the following are three primes: p1 = 43 * 44 / 2 + 1 = 947. p2 = 947 * 948 / 2 + 1 = 448879. p3 = 448879 * 448880 / 2 + 1 = 100746402761. CROSSREFS Cf. A000040, A000217, A034953, A231847, A231988. Sequence in context: A308645 A086889 A269909 * A059495 A174325 A290366 Adjacent sequences: A231986 A231987 A231988 * A231990 A231991 A231992 KEYWORD nonn,hard,more AUTHOR Alex Ratushnyak, Nov 16 2013 STATUS approved

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Last modified March 29 05:02 EDT 2023. Contains 361596 sequences. (Running on oeis4.)