A089329 Smallest k such that the concatenation r*k for r = 1 to n followed by a 1 is a prime.

1, 2, 1, 7, 2, 2, 24, 8, 1, 103, 1, 12, 43, 94, 21, 1, 11, 12, 4, 23, 27, 4, 89, 20, 42, 1, 43, 6, 41, 44, 190, 22, 12, 139, 41, 114, 16, 3, 26, 171, 32, 220, 78, 86, 135, 117, 21, 44, 49, 143, 248, 175, 9, 76, 6, 66, 426, 46, 237, 252, 9, 62, 319, 88, 150, 123, 61, 122, 300, 15

Offset

1,2

Links

Table of n, a(n) for n=1..70.

Example

a(4) = 7 and the prime is 71421281 = A089328(4).

Mathematica

Do[s = ""; k = 0; While[ !PrimeQ[ToExpression[s]], s = ""; k++; For[r = 1, r <= n, r++, s = s <> ToString[r*k]]; s = s <> "1"]; Print[k], {n, 1, 50}] (* Ryan Propper, Jul 24 2005 *)

Crossrefs

Cf. A089328.

Sequence in context: A144446 A121416 A317547 * A213053 A200236 A292191

Adjacent sequences: A089326 A089327 A089328 * A089330 A089331 A089332

Keyword

base,nonn

Author

Amarnath Murthy, Nov 04 2003

Extensions

Corrected and extended by Ryan Propper, Jul 24 2005

More terms from David Wasserman, Sep 13 2005

Status

approved