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 A005115 Let i, i+d, i+2d, ..., i+(n-1)d be an n-term arithmetic progression of primes; choose the one which minimizes the last term; then a(n) = last term i+(n-1)d. (Formerly M0854) 25
 2, 3, 7, 23, 29, 157, 907, 1669, 1879, 2089, 249037, 262897, 725663, 36850999, 173471351, 198793279, 4827507229, 17010526363, 83547839407, 572945039351, 6269243827111 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS In other words, smallest prime which is at the end of an arithmetic progression of n primes. For the corresponding values of the first term and the common difference, see A113827 and A093364. For the actual arithmetic progressions, see A133277. One may also minimize the common difference: this leads to A033189, A033188 and A113872. One may also specify that the first term is the n-th prime and then minimize the common difference (or, equally, the last term): this leads to A088430 and A113834. One may also ask for n consecutive primes in arithmetic progression: this gives A006560. REFERENCES R. K. Guy, Unsolved Problems in Number Theory, A5. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Jens Kruse Andersen, Primes in Arithmetic Progression Records [May have candidates for later terms in this sequence.] H. Dubner and H. Nelson, Seven consecutive primes in arithmetic progression, Math. Comp., 66 (1997) 1743-1749. MR 98a:11122. Ben Green and Terence Tao, The primes contain arbitrarily long arithmetic progressions, Annals of Mathematics 167 (2008), pp. 481-547. arXiv:math/0404188 [math.NT], 2004-2007. Ben Green and Terence Tao, A bound for progressions of length k in the primes Andrew Granville, Prime number patterns, American Mathematical Monthly 115 (2008), pp. 279-296. A. Moran, P. Pritchard and A. Thyssen, Twenty-two primes in arithmetic progression, Math. Comp.64 (1995), no.211, 1337-1339. FORMULA Green & Tao prove that this sequence is infinite, and further a(n) < 2^2^2^2^2^2^2^2^O(n). Granville conjectures that a(n) <= n! + 1 for n >= 3 and give a heuristic suggesting a(n) is around (exp(1-gamma) n/2)^(n/2). - Charles R Greathouse IV, Feb 26 2013 EXAMPLE n, AP, last term 1 2 2 2 2+j 3 3 3+2j 7 4 5+6j 23 5 5+6j 29 6 7+30j 157 7 7+150j 907 8 199+210j 1669 9 199+210j 1879 10 199+210j 2089 11 110437+13860j 249037 12 110437+13860j 262897 .......................... a(11)=249037 since 110437,124297,...,235177,249037 is an arithmetic progression of 11 primes ending with 249037 and it is the least number with this property. MATHEMATICA (* This program will generate the 4 to 12 terms to use a[n_] to generate term 13 or higher, it will have a prolonged run time. *) a[n_] := Module[{i, p, found, j, df, k}, i = 1; While[i++; p = Prime[i]; found = 0; j = 0; While[j++; df = 6*j; (p > ((n - 1)*df)) && (found == 0), found = 1; Do[If[! PrimeQ[p - k*df], found = 0], {k, 1, n - 1}]]; found == 0]; p]; Table[a[i], {i, 4, 12}] CROSSREFS For the associated gaps, see A093364. For the initial terms, see A113827. For the arithmetic progressions, see A133277. Cf. A006560, A096003, A113830-A113834, A088430. Sequence in context: A156615 A158054 A134412 * A113872 A120302 A093363 Adjacent sequences:  A005112 A005113 A005114 * A005116 A005117 A005118 KEYWORD nonn,hard,more,nice AUTHOR EXTENSIONS a(11)-a(13) from Michael Somos, Mar 14 2004 a(14) and corrected version of a(7) from Hugo Pfoertner, Apr 27 2004 a(15)-a(17) from Don Reble, Apr 27 2004 a(18)-a(21) from Granville's paper, Jan 26 2006 Entry revised by N. J. A. Sloane, Jan 26 2006, Oct 17 2007 STATUS approved

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Last modified October 20 07:33 EDT 2019. Contains 328252 sequences. (Running on oeis4.)