A114780 Least multiple of 2n-1 ending in prime(n), 0 if no such number exists.

2, 3, 5, 7, 711, 913, 117, 0, 323, 1729, 231, 437, 0, 243, 1247, 1953, 759, 0, 3367, 3471, 2173, 2279, 0, 4089, 2597, 28101, 45103, 0, 2109, 18113, 43127, 40131, 0, 1139, 22149, 34151, 37157, 0, 13167, 62173, 37179, 17181, 0, 38193, 33197, 17199, 86211

Offset

1,1

Comments

If prime(n) has k digits then a(n) == prime(n) (mod 10^k); a(8r+5) = 0 for r > 1.

Links

Table of n, a(n) for n=1..47.

Example

a(5) = 711, ending in 11 = prime(n) and 711 == 0 (mod 9, the fifth odd number).

Prog

(PARI) a(n) = {if (((n >=8) && ((n-8) % 5 == 0)), return (0)); k = 1; tn = 2*n-1; p = prime(n); tp = 10^length(Str(p)); while ((k*tn) % tp != p, k++); return (k*tn); } \\ Michel Marcus, Sep 15 2013

Crossrefs

Cf. A114781.

Sequence in context: A360789 A145843 A090720 * A241681 A134811 A046479

Adjacent sequences: A114777 A114778 A114779 * A114781 A114782 A114783

Keyword

base,nonn

Author

Amarnath Murthy, Nov 17 2005

Extensions

More terms from Joshua Zucker, May 05 2006

Status

approved