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 A185685 Irregular triangle, read by rows, of primes with prefix n and digits "7" appended, otherwise 0. 7
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Row n ends when a composite number is found. LINKS 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: A002488 A243776 A198631 * A144692 A241027 A176728 Adjacent sequences:  A185682 A185683 A185684 * A185686 A185687 A185688 KEYWORD nonn,base,less,tabf AUTHOR Michel Lagneau, Feb 10 2011 STATUS approved

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