A140515 Numbers n such that one of floor(10^n * Pi) or ceiling(10^n * Pi) is prime.

0, 1, 5, 11, 18, 37, 601, 1901, 2394, 3970, 5826, 16207

Offset

1,3

Links

Table of n, a(n) for n=1..12.

Carlos B. Rivera F. Puzzle 50. Approximation to pi with primes, The Prime Puzzles and Problems Connection.

Eric Weisstein's World of Mathematics, Pi Digits

Example

ceiling(10^11*Pi) = ceiling(314159265358.9...) = 314159265359 is prime, so 11 is in the sequence.

Mathematica

npQ[n_]:=Module[{c=10^n Pi}, Total[Boole[PrimeQ[{Floor[ c], Ceiling[ c]}]]] == 1]; Select[Range[0, 4000], npQ] (* The program generates the first 10 terms of the sequence. To generate more, increase the Range constant, but the program may take a long time to run. *) (* Harvey P. Dale, May 07 2021 *)

Prog

(PARI) isA140515(n)=isprime(bitor(floor(10^n*Pi), 1))

Crossrefs

Sequence in context: A140697 A048253 A102174 * A349553 A056996 A102184

Adjacent sequences: A140512 A140513 A140514 * A140516 A140517 A140518

Keyword

nonn,base,more

Author

Marvin Ray Burns, Jul 01 2008, Jul 02 2008

Status

approved