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A112534
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Number of digits in A110778(n).
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6
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1, 1, 1, 3, 3, 21, 7, 31, 5, 480, 1526, 294, 1615
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,4
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LINKS
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EXAMPLE
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MATHEMATICA
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id[n_]:=IntegerDigits[n]; f[x_, y_]:=FromDigits[Flatten[Append[{x}, y]]]; a[x_, y_]:=NestWhile[f[id[#], y]&, f[id[x], y], !PrimeQ[#]&]; le[n_]:=Length[id[n]]; d[x_, y_]:=x-FromDigits[PadRight[id[y], le[x]]]; x=3; t={1}; Do[y=a[x, 7]; AppendTo[t, le[d[y, x]]]; x=a[y, 3]; AppendTo[t, le[d[x, y]]], {n, 5}]; t (* Jayanta Basu, May 20 2013 *)
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PROG
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(Python)
from sympy import isprime
from itertools import count, islice
def agen(): # generator of terms
s = ""
while True:
for d in "37":
for k in count(1):
if isprime(int(s+d*k)): break
yield k
s += d*k
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CROSSREFS
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Cf. A110774, A110775, A110776, A110777, A110778, A110780, A110781, A110782, A110783, A110788, A110789.
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KEYWORD
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base,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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