login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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

Table of n, a(n) for n=1..11.

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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified February 21 04:43 EST 2018. Contains 299389 sequences. (Running on oeis4.)