A185685 Irregular triangle, read by rows, of primes with prefix n and digits "7" appended, otherwise 0.

17, 0, 37, 47, 0, 67, 677, 0, 0, 97, 977, 107, 0, 127, 1277, 137, 0, 157, 167, 0, 0, 197, 0, 0, 227, 0, 0, 257, 0, 277, 2777, 0, 0, 307, 317, 0, 337, 347, 0, 367, 3677, 0, 0, 397, 0, 0, 0, 0, 0, 457, 467, 0, 487, 4877, 0, 0, 0, 0, 0, 547, 5477, 557, 0, 577, 587, 0, 607, 617, 0, 0

Offset

1,1

Comments

Row n ends when a composite number is found.

Links

Table of n, a(n) for n=1..70.

Example

for k=1..2 , a(12,k) = {127, 1277} 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+7: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, 7]]; PrimeQ[p], cnt++; Sow[p]]; If[cnt == 0, Sow[0]], {n, 61}]][[2, 1]]

Crossrefs

Cf. A185682, A185684.

Sequence in context: A243776 A338801 A198631 * A144692 A335264 A241027

Adjacent sequences: A185682 A185683 A185684 * A185686 A185687 A185688

Keyword

nonn,base,less,tabf

Author

Michel Lagneau, Feb 10 2011

Status

approved