A186071 - OEIS

%I #8 Jan 25 2013 09:07:37

%S 31,331,3331,33331,333331,3333331,33333331,0,0,0,0,0,37,337,0,0,0,311,

%T 0,313,3313,0,0,0,317,0,0,0,0,0,0,0,0,0,0,0,0,0,331,3331,33331,333331,

%U 3333331,33333331,0,0,0,0,0,337,0,0,0,0,0,0,0,0,0,347,3347,33347,0,349,0,0,0,353

%N Irregular triangle, read by rows, of primes with suffix n and digits "3" prepended , otherwise 0.

%C Row n ends when a composite number is found.

%e for k=1..7 , a(1, k) = {31, 331, 3331, 33331, 333331, 3333331, 33333331} are in the sequence.

%p with(numtheory): for n from 1 to 100 do:a0:=n:id:=0:c:=0:for k from 1 to 20

%p   while (id=0) do:d:=length(a0):a1:=3*10^d+a0:if type(a1, prime)=true then a0:=a1:printf(`%d,

%p   `, a0):c:=c+1:else id:=1:fi:od:if c=0 then printf(`%d, `, 0):else fi:od:

%Y Cf. A185682, A185684, A185685, A185687.

%K nonn,base,tabf

%O 1,1

%A _Michel Lagneau_, Feb 11 2011