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%I #19 Jul 28 2022 03:48:12
%S 11,0,31,311,41,0,61,71,0,0,101,0,0,131,0,151,1511,0,0,181,1811,191,0,
%T 211,2111,0,0,241,2411,251,0,271,2711,281,0,0,311,0,331,0,0,0,0,0,0,
%U 401,0,421,4211,431,0,0,461,0,0,491,0,0,521,0,541,0,0,571,5711,0,0,601,6011,0,0
%N Irregular triangle, read by rows, of primes with prefix n and digits "1" appended, otherwise 0.
%C Row n ends when a composite number is found.
%e For k=1..2, a(15, k) = {151, 1511} 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:a1:=a0*10+1:if type(a1,prime)=true then a0:=a1:printf(`%d, `,a0):c:=c+1:else
%p id:=1:fi:od:if c=0 then printf(`%d, `,0):else fi:od:~
%t Reap[Do[cnt = 0; d = IntegerDigits[n]; While[p = FromDigits[AppendTo[d, 1]]; PrimeQ[p], cnt++; Sow[p]]; If[cnt == 0, Sow[0]], {n, 61}]][[2, 1]]
%Y Cf. A069568 (least number of 1's to append to n to make a prime).
%K nonn,base,less,tabf
%O 1,1
%A _Michel Lagneau_, Feb 10 2011
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