A114740 Smallest prime == 2n-1 (mod composite(2n-1)), or 0 if impossible.

5, 3, 5, 7, 41, 11, 13, 0, 17, 19, 0, 23, 101, 67, 29, 31, 131, 137, 37, 151, 41, 43, 109, 47, 463, 0, 53, 0, 137, 59, 61, 0, 0, 67, 163, 71, 73, 0, 0, 79, 0, 83, 317, 677, 89, 457, 0, 347, 97, 0, 101, 103, 0, 107, 109, 257, 113, 419, 271, 431, 439, 1733, 617, 127, 467, 131

Offset

1,1

Links

Table of n, a(n) for n=1..66.

Example

a(8)=0 because the 15th composite is 30 and no prime is congruent to 15 (mod 30).

Mathematica

f[n_] := Block[{k = 1, m = FixedPoint[2n + PrimePi[ # ] &, 2n - 1]}, While[k < 100000 && Mod[Prime[k], m] != 2n - 1, k++ ]; If[k == 100000, 0, Prime[k]]]; Table[ f[n], {n, 67}] (* Robert G. Wilson v *)

Crossrefs

Sequence in context: A131925 A128010 A185046 * A330523 A379338 A361546

Adjacent sequences: A114737 A114738 A114739 * A114741 A114742 A114743

Keyword

nonn

Author

Amarnath Murthy, Nov 15 2005

Extensions

Corrected and extended by Robert G. Wilson v, Nov 17 2005

Status

approved