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

1,1

Comments

Row n ends when a composite number is found.

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

Links

Table of n, a(n) for n=1..71.

Example

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;
  ...

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]]

Crossrefs

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

Sequence in context: A256756 A087558 A087555 * A217752 A335646 A261173

Adjacent sequences: A185679 A185680 A185681 * A185683 A185684 A185685

Keyword

nonn,base,less,tabf,changed

Author

Michel Lagneau, Feb 10 2011

Status

approved