A185685 - OEIS

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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

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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