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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Row n ends when a composite number is found.

LINKS

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

EXAMPLE

For k=1..2, a(15, k) = {151, 1511} are in the sequence.

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

AUTHOR

Michel Lagneau, Feb 10 2011

STATUS

approved

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Last modified September 29 16:10 EDT 2022. Contains 357090 sequences. (Running on oeis4.)