A282183 Numbers k such that the reverse of the first k digits in the decimal expansion of Pi forms a prime.

1, 2, 5, 6, 7, 11, 15, 712, 7599, 13280

Offset

1,2

Comments

The initial digits of a few corresponding primes are in A007523. The last one a(10)=768556......62951413 is a prime with 13280-digit. That is A092845(13279).

Links

Table of n, a(n) for n=1..10.

Example

1 is a term as the first digit of pi, 3, reversed is prime. 2 is a term as the first two digits of pi, 31, reversed is prime. 3 is not a term as the first three digits of pi, 314, reversed, is not prime. - David A. Corneth, Feb 13 2017

Mathematica

Do[If[PrimeQ[FromDigits[Reverse[IntegerDigits[Floor[Pi*10^(n - 1)]]]]], Print[n]], {n, 13335}]
Module[{pid=RealDigits[Pi, 10, 20000][[1]]}, Select[Range[16000], PrimeQ[ FromDigits[ Reverse[Take[pid, #]]]]&]] (* Harvey P. Dale, Sep 06 2019 *)

Crossrefs

Cf. A092845, A007523, A011545.

Sequence in context: A043329 A023699 A058605 * A103025 A134080 A342792

Adjacent sequences: A282180 A282181 A282182 * A282184 A282185 A282186

Keyword

nonn,more,base,less

Author

XU Pingya, Feb 13 2017

Status

approved