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 A084435 a(1) = 2, then smallest prime of the form 2^k*a(n-1) + 1. 2
 2, 3, 7, 29, 59, 1889, 3779, 7559, 4058207223809, 32465657790473, 4462046030502692971872257, 9582170887127842377060195852353537 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This sequence also is generated when the initial term is 1. It is unclear if the sequence is finite or infinite. - Bob Selcoe, Oct 09 2015 REFERENCES Donald E. Knuth, The Art of Computer Programming, Vol. 2, Seminumerical Algorithms, problem 39, page 76. LINKS Robert G. Wilson v, Table of n, a(n) for n = 1..15 (shortened by N. J. A. Sloane, Jan 13 2019) EXAMPLE a(3)=7 because 3*2+1=7 is prime; a(4)=29 because 7*2+1=15 is not prime, 7*4+1=29 is prime. MATHEMATICA f[s_List] := Block[{k = 0, p = s[[-1]]}, While[q = 2^k*p + 1; !PrimeQ[ q], k++]; Append[s, q]]; s = {2}; Nest[f, s, 16] (* Robert G. Wilson v, Mar 11 2015 *) PROG (PARI) lista(nn) = {a = 2; print1(a, ", "); for (n=1, nn, k=0; while (!isprime(2^k*a+1), k++); a = 2^k*a+1; print1(a, ", "); ); } \\ Michel Marcus, Mar 18 2015 CROSSREFS Cf. A113767, A192580. Sequence in context: A062573 A019435 A061092 * A072469 A004062 A037151 Adjacent sequences:  A084432 A084433 A084434 * A084436 A084437 A084438 KEYWORD nonn AUTHOR Amarnath Murthy, Jun 03 2003 STATUS approved

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Last modified August 3 01:55 EDT 2021. Contains 346429 sequences. (Running on oeis4.)