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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 (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 Cf. A065828 up to A065839, A000796, A011545, A011546, A055145, A005042, A060421, A039954, A048796. Sequence in context: A245001 A007569 A054317 * A181934 A093785 A105369 Adjacent sequences:  A065837 A065838 A065839 * A065841 A065842 A065843 KEYWORD nonn,base,hard AUTHOR Patrick De Geest, Nov 24 2001 STATUS approved

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Last modified October 16 08:40 EDT 2018. Contains 316259 sequences. (Running on oeis4.)