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 A173937 Smallest natural d = d(n) such that 2^n + d is lesser of twin primes (n = 0, 1, 2, ...). 3
 2, 1, 1, 3, 1, 9, 7, 9, 13, 9, 7, 33, 31, 27, 67, 33, 1, 39, 7, 63, 313, 105, 277, 9, 73, 69, 457, 51, 121, 105, 7, 219, 91, 297, 247, 321, 115, 567, 1327, 411, 553, 987, 325, 183, 2065, 2565, 415, 879, 241, 459, 643, 1209, 391, 1155, 1477, 1449, 175, 129, 1045 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 REFERENCES Richard K. Guy, Unsolved Problems in Number Theory, New York, Springer-Verlag, 1994 Friedhelm Padberg, Elementare Zahlentheorie, Spektrum Akademischer Verlag, Berlin Heidelberg, 1996 Daniel Shanks, Solved and Unsolved Problems in Number Theory, 4th ed., New York, Chelsea, 1993 LINKS T. D. Noe, Table of n, a(n) for n = 0..300 Ken Takusagawa, Twin primes EXAMPLE 2^0 + 2 = 3 = prime(2), 2^0 + 4 = 5 = prime(3). 2^1 + 1 = 3 = prime(2), 2^1 + 3 = 5 = prime(3). 2^2 + 1 = 5 = prime(3), 2^2 + 3 = 7 = prime(4). MATHEMATICA Join[{2}, Table[s = 2^n + 1; While[! (PrimeQ[s] && PrimeQ[s + 2]), s = s + 2]; s - 2^n, {n, 60}]] (* T. D. Noe, May 08 2012 *) PROG (PARI) A173937(n)={forstep(p=2^n\6*6+5, 2< 2^n). Sequence in context: A003687 A104575 A318833 * A046223 A192181 A073463 Adjacent sequences:  A173934 A173935 A173936 * A173938 A173939 A173940 KEYWORD nonn AUTHOR Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Mar 03 2010 EXTENSIONS Values a(0..300) double-checked by M. F. Hasler, Oct 21 2012 STATUS approved

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Last modified October 17 16:31 EDT 2019. Contains 328117 sequences. (Running on oeis4.)