A287294 Concatenation of sequence (2n-1,2n-3,..,3,1,3,..,2n-3,2n-1).

1, 313, 53135, 7531357, 975313579, 1197531357911, 13119753135791113, 151311975313579111315, 1715131197531357911131517, 19171513119753135791113151719, 211917151311975313579111315171921, 2321191715131197531357911131517192123

Offset: 1

Author

XU Pingya, May 22 2017

Keywords

• base
• easy
• nonn

Comments

For n <= 1400, a(2) = 313, a(10) = 19171513119753135791113151719, a(12) = 2321191715131197531357911131517192123 and a(110) = 219217..313..217219 are primes.

Links

• F. Smarandache, Sequences of Numbers Involved in Unsolved Problems.
• Eric Weisstein's World of Mathematics, Smarandache Sequences

Crossrefs

Cf. A007942.

Programs

Mathematica

Block[{nn = 12, s}, s = IntegerDigits@ Range[1, 2 nn - 1, 2]; Table[FromDigits@ Flatten@ Join[Reverse[Rest@ #], #] &@ Take[s, n], {n, nn}]] (* Michael De Vlieger, May 23 2017 *)