A185682 Irregular triangle, read by rows, of primes with prefix n and digits "1" appended, otherwise 0.

11, 0, 31, 311, 41, 0, 61, 71, 0, 0, 101, 0, 0, 131, 0, 151, 1511, 0, 0, 181, 1811, 191, 0, 211, 2111, 0, 0, 241, 2411, 251, 0, 271, 2711, 281, 0, 0, 311, 0, 331, 0, 0, 0, 0, 0, 0, 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

Offset: 1

Author

Michel Lagneau, Feb 10 2011

Keywords

• nonn
• base
• less
• tabf

Comments

Row n ends when a composite number is found.

No row has more than two terms. - Robert Israel, Sep 06 2024

Examples

			For k=1..2, a(15, k) = {151, 1511} are in the sequence.
Triangle begins:
   11;
    0;
   31, 311;
   41;
    0;
   61;
   71;
    0;
    0;
  101;
  ...
		

Crossrefs

Cf. A069568 (least number of 1's to append to n to make a prime).

Programs

Maple

with(numtheory): for n from 1 to 100 do:a0:=n:id:=0:c:=0:for k from 1 to 20
  while (id=0) do:a1:=a0*10+1:if type(a1,prime)=true then a0:=a1:printf(`%d, `,a0):c:=c+1:else
  id:=1:fi:od:if c=0 then printf(`%d, `,0):else fi:od:~

Mathematica

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]]