A109550 Primes of the form aaaa...aa1 where a is 3, 4, 5, 6 or 7.

31, 41, 61, 71, 331, 661, 3331, 4441, 6661, 33331, 333331, 3333331, 33333331, 6666666661, 44444444441, 555555555551, 5555555555551, 7777777777771, 333333333333333331, 666666666666666661, 77777777777777777771

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..52

Formula

d=3, 4, 5, 6, 7 a(n) = if prime then Sum[d*10^i, {i, 1, m}] + 1

Mathematica

d[n_] = If[2 + Mod[n, 6] > 0, 2 + Mod[n, 6], 1] a = Flatten[Table[Sum[d[k]*10^i, {i, 1, m}] + 1, {m, 1, 50}, {k, 1, 4}]] b = Flatten[Table[If[PrimeQ[a[[i]]] == True, a[[i]], {}], {i, 1, Length[a]}]]
Select[FromDigits/@Flatten[Table[PadLeft[{1}, i, #]&/@{3, 4, 5, 6, 7}, {i, 2, 100}], 1], PrimeQ[#]&] (* Vincenzo Librandi, Dec 12 2011 *)

Crossrefs

Cf. A051200, A004022, A093176, A093177, A089346, A093174, A092571, A089345, A089347.

Sequence in context: A040178 A089719 A340444 * A040991 A089721 A089442

Adjacent sequences: A109547 A109548 A109549 * A109551 A109552 A109553

Keyword

nonn

Author

Roger L. Bagula, Jun 26 2005

Status

approved