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 A112750 Smallest prime of the form 7 followed by j copies of the digit k, where j runs through those positive values for which such a prime exists. 0
 71, 733, 7333, 79999, 733333, 71111111, 799999999, 79999999999, 79999999999999999999999999, 79999999999999999999999999999999999999999999999999, 733333333333333333333333333333333333333333333333333333, 71111111111111111111111111111111111111111111111111111111 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For all j > 0, k must be 1, 3, or 9, since a number with -- -- digits 7kk...kk where k is even will be a proper multiple of 2; -- digits 755...55 will be a proper multiple of 5; and -- digits 777...77 will be a proper multiple of 7. LINKS Table of n, a(n) for n=1..12. EXAMPLE 7333 is a term because it is prime and is 7 followed by three copies of 3, and the numbers 7000, 7111, and 7222 are all nonprime. From Jon E. Schoenfield, Feb 23 2021: (Start) Terms begin as follows: n j k a(n) -- -- - -------------------------------------------------------- 1 1 1 71 2 2 3 733 3 3 3 7333 4 4 9 79999 5 5 3 733333 - 6 - (7111111, 7333333, 7999999 are composite) 6 7 1 71111111 7 8 9 799999999 - 9 - (7111111111, 7333333333, 7999999999 are composite) 8 10 9 79999999999 - 11 - (711111111111, 733333333333, 799999999999 are composite) - 12 - (all composite) - 13 - (all composite) ... 9 25 9 79999999999999999999999999 ... 10 49 9 79999999999999999999999999999999999999999999999999 ... 11 53 3 733333333333333333333333333333333333333333333333333333 12 55 1 71111111111111111111111111111111111111111111111111111111 (End) MATHEMATICA SelectFirst[#, PrimeQ]&/@Table[FromDigits[PadRight[{7}, n, p]], {n, 2, 60}, {p, {1, 3, 9}}]/.Missing["NotFound"]->Nothing (* Harvey P. Dale, Apr 19 2021 *) CROSSREFS Subset of A090155. Sequence in context: A180327 A201039 A142674 * A351896 A089706 A220623 Adjacent sequences: A112747 A112748 A112749 * A112751 A112752 A112753 KEYWORD base,nonn,less AUTHOR Amarnath Murthy, Jan 02 2006 EXTENSIONS More terms added by Harvey P. Dale, Jan 24 2010 Name corrected (using a suggestion from Felix Fröhlich) and Example edited by Jon E. Schoenfield, May 28 2019 Terms corrected by Jon E. Schoenfield, Feb 23 2021 STATUS approved

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Last modified March 4 02:53 EST 2024. Contains 370522 sequences. (Running on oeis4.)