A231336 - OEIS

A231336

Integers n such that appending some decimal digit to the first n digits of Pi results in a prime.

0, 1, 2, 5, 11, 12, 18, 37, 39, 77, 82, 100, 125, 128, 220, 305, 601, 676, 1692, 1901, 2202, 2253, 2394, 3318, 3970, 5826, 7001, 9853, 12607, 13434, 16207

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OFFSET

1,3

COMMENTS

A140515 is a proper subsequence. A060421 - 1 is a proper subsequence. So the terms 47576 & 78072 are also members.

LINKS

Table of n, a(n) for n=1..31.

EXAMPLE

0 is in the sequence since 2, 3, 5, and 7 are all primes;

1 is in the sequence since 31 and 37 are both primes;

2 is in the sequence since 311, 313, and 317 are all primes;

3 is not in the sequence since 3141, 3143, 3147, and 3149 are all composites;

4 is not in the sequence since 31411, 31413, 31417, and 31419 are all composites;

5 is in the sequence since 314159 is a prime; etc.

MATHEMATICA

fQ[n_] := Union[PrimeQ[ 10 IntegerPart[10^n*Pi] + {1, 3, 7, 9}]][[-1]]; k = -1; lst = {}; While[k < 17001, If[ fQ@ k, AppendTo[lst, k + 1]; Print[k + 1]]; k++]; lst

Module[{nn=16300, pd}, pd=RealDigits[Pi, 10, nn][[1]]; Select[Range[0, nn], AnyTrue[ 10*FromDigits[Take[pd, #]]+{1, 3, 7, 9}, PrimeQ]&]] (* Harvey P. Dale, Aug 14 2022 *)

PROG

(PARI) is(n)=my(d=Pi*10^n\10*10); isprime(d+1) || isprime(d+3) || isprime(d+7) || isprime(d+9) \\ Charles R Greathouse IV, Nov 07 2013

CROSSREFS

Cf. A140515, A060421, A005042.

Sequence in context: A136991 A136989 A136987 * A283473 A062889 A065433

Adjacent sequences: A231333 A231334 A231335 * A231337 A231338 A231339

KEYWORD

nonn,base

AUTHOR

Marvin Ray Burns and Robert G. Wilson v, Nov 07 2013

EXTENSIONS

Keyword "base" added by Zak Seidov, Nov 11 2013

STATUS

approved