A110680 Numbers k such that the string 4444k is prime.

9, 21, 43, 49, 61, 63, 69, 73, 87, 109, 127, 147, 159, 169, 171, 201, 207, 213, 217, 229, 241, 261, 289, 291, 331, 339, 357, 369, 381, 397, 409, 469, 471, 483, 487, 507, 519, 549, 591, 607, 621, 639, 663, 669, 697, 703, 711, 717, 729, 747

Offset: 1

Author

Parthasarathy Nambi, Sep 14 2005

Keywords

• nonn
• base

Examples

			k=109 is in the sequence because 4444k = 4444109 is prime.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Programs

Mathematica

Select[Range[800],PrimeQ[4444*10^IntegerLength[#]+#]&] (* Harvey P. Dale, Jul 04 2014 *)