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A065575
Numbers k such that the first k septenary digits found in the decimal expansion of Pi form a prime.
1
1, 15, 31, 575, 736, 1733, 2282, 26818, 44456
OFFSET
1,2
COMMENTS
No additional terms through k = 5000. - Harvey P. Dale, Aug 25 2019
Any further terms are > 100000. - Lucas A. Brown, Oct 24 2024
MATHEMATICA
p = First[ RealDigits[ Pi, 10, 10^5]]; p = p[[ Select[ Range[10^5], p[[ # ]] == 0 || p[[ # ]] == 1 || p[[ # ]] == 2 || p[[ # ]] == 3 || p[[ # ]] == 4 || p[[ # ]] == 5 || p[[ # ]] == 6 & ]]]; Do[ If[ PrimeQ[ FromDigits[ Take[p, n], 7]], Print[n]], {n, 1, 2500} ]
With[{pi7=Select[RealDigits[Pi, 10, 5000][[1]], #<7&]}, Select[Range[ 2300], PrimeQ[ FromDigits[Take[pi7, #], 7]]&]] (* Harvey P. Dale, Aug 25 2019 *)
CROSSREFS
Sequence in context: A041444 A041446 A042853 * A041448 A157767 A146889
KEYWORD
nonn,base,hard,more,changed
AUTHOR
Robert G. Wilson v, Dec 01 2001
EXTENSIONS
a(8)-a(9) from Lucas A. Brown, Oct 24 2024
STATUS
approved