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A185682
Irregular triangle, read by rows, of primes with prefix n and digits "1" appended, otherwise 0.
9
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
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
KEYWORD
nonn,base,less,tabf
AUTHOR
Michel Lagneau, Feb 10 2011
STATUS
approved