A075616 - OEIS

A075616

Rearrangement of natural numbers so that starting with a(n) the concatenation of n numbers gives a prime.

%I #4 Dec 05 2013 19:55:39

%S 2,1,3,4,7,5,9,6,17,8,43,10,19,11,13,12,33,14,37,15,23,16,113,18,73,

%T 20,51,21,103,22,61,24,87,25,49,26,67,27,117,28,57,29,71,30,79,31,283,

%U 32,239,34,81,35,143,36,151,38,139,39,147,40,289,41,161,42,351,44,129,45

%N Rearrangement of natural numbers so that starting with a(n) the concatenation of n numbers gives a prime.

%t a = {2, 1, 3}; f[n_] := Block[{k = 1, b = Take[a, {n, 2n - 3}]}, While[Position[a, k] != {}, k++ ]; b = Join[b, IntegerDigits[k]]; a = Append[a, k]; While[ Position[a, k] != {} || !PrimeQ[ FromDigits[ Join[ b, IntegerDigits[k]]]], k++ ]; a = Append[a, k]]; Do[ f[n], {n, 3, 40}]; a

%Y Cf. A075617 and A073672.

%K base,nonn

%O 1,1

%A _Amarnath Murthy_, Sep 29 2002

%E Edited and extended by _Robert G. Wilson v_, Oct 02 2002