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A065840
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Numbers n such that the first n quaternary digits found in the base-10 expansion of pi form a prime (when the decimal point is ignored).
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12
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1, 2, 3, 5, 10, 19, 72, 115, 220, 315, 375
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| In other words, take the decimal expansion of pi, drop any digits greater than 4, omit the decimal point and look for prefixes in the resulting string which form base-4 primes.
Numbers n such that A065838(n) is prime.
The next term in the sequence, if it exists, is greater than 10000. - Nathaniel Johnston (nathaniel(AT)nathanieljohnston.com), Nov 15 2010
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EXAMPLE
| E.g. the first a(5) or 10 quaternary digits of pi are 31.12332323{4} and 3112332323{4} is the prime 880571{10}.
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MATHEMATICA
| p = First[ RealDigits[ Pi, 10, 10^5]]; p = p[[ Select[ Range[10^5], p[[ # ]] == 0 || p[[ # ]] == 1 || p[[ # ]] == 2 || p[[ # ]] == 3 & ]]]; Do[ If[ PrimeQ[ FromDigits[ Take[p, n], 4]], Print[ n]], {n, 1, 4000} ]
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CROSSREFS
| Cf. A065828 up to A065839, A000796, A011545, A011546, A055145, A005042, A060421, A039954, A048796.
Sequence in context: A064236 A007569 A054317 * A093785 A105369 A047101
Adjacent sequences: A065837 A065838 A065839 * A065841 A065842 A065843
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KEYWORD
| nonn,base,hard
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AUTHOR
| Patrick De Geest (pdg(AT)worldofnumbers.com), Nov 24 2001.
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