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A065840 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). 12
1, 2, 3, 5, 10, 19, 72, 115, 220, 315, 375, 12408 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
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, Nov 15 2010
LINKS
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}.
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} ]
CROSSREFS
Sequence in context: A365858 A007569 A054317 * A181934 A093785 A105369
KEYWORD
nonn,base,hard
AUTHOR
Patrick De Geest, Nov 24 2001
EXTENSIONS
a(12) from Chai Wah Wu, Apr 07 2020
STATUS
approved

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Last modified March 19 03:33 EDT 2024. Contains 370952 sequences. (Running on oeis4.)