A186073 - OEIS

%I #5 Mar 30 2012 18:35:54

%S 71,0,73,773,0,0,0,0,0,79,0,0,0,0,0,0,0,0,0,719,0,0,0,0,0,0,0,727,

%T 7727,0,0,0,0,0,733,0,0,0,0,0,739,0,0,0,743,0,0,0,0,0,0,0,751,0,0,0,0,

%U 0,757,7757,0,0,0,761,0,0,0,0,0,0,0,769,0,0,0,773

%N Irregular triangle, read by rows, of primes with suffix n and digits "7" prepended, otherwise 0.

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

%e for k=1..2 , a(3, k) = {73, 773} 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:=7*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. A186071  A186072  A185682  A185684  A185685  A185687.

%K nonn,base,tabf

%O 1,1

%A _Michel Lagneau_, Feb 11 2011