**A search for ten consecutive primes in arithmetic progression**

The primes are

*P* = 100 99697 24697 14247 63778 66555 87969 84032 95093 24689 19004
18036 03417 75890 43417 03348 88215 90672 29719,

*P* + 210, *P* + 420, *P* + 630, *P* + 840, *P*
+ 1050, *P* + 1260, *P* + 1470,
*P* + 1680 and *P* + 1890.

On August 29 1995, Harvey Dubner and Harry Nelson discovered
seven
consecutive primes in arithmetic progression, namely *p*, *p* +
210, *p* + 420, *p* + 630, *p* + 840, *p* + 1050 and
*p* + 1260 where *p* is the 97-digit number:

1089533431247059310875780378922957732908036492993138195385213105561742150447308967213141717486151.

On 7 November 1997, we - Harvey Dubner, Tony Forbes, Nik Lygeros, Michel Mizony and Paul Zimmermann - announced the discovery of eight consecutive primes in arithmetic progression after a search lasting a couple of months using a variety of PC's and Unix workstations.

We then initiated a search for nine primes, calling on the help of about a
hundred people world-wide and using about 200 computers. On 15 January 1998,
this search ended successfully when **Manfred Toplic** of Klagenfurt, Austria, found
nine
consecutive primes in arithmetic progression using Tony's program CP09.EXE
on a PC.

Immediately we started to look for **ten consecutive primes in arithmetic
progression**. Although much more difficult, it was nevertheless quite
feasible. We estimated about 300 years, assuming computers search at the rate of
1200 million numbers per hour. Therefore we thought we would need a lot of help.

We looked for special candidates of the form
*p* = *N* *m* + *x*, where

*x* = 54538241683887582668189703590110659057865934764604873840781923513421103495579,

*m* = 193#, the product of the 44 primes up to 193, and *N* = 0,
1, 2, ....

We think we were unlucky with nine primes; the search took considerably
longer than we anticipated. The probability calculation for ten primes suggests
that we should expect success after about 3000 trillion *N*s, give
or take a quadrillion or two. Well, as you have seen, this time we good fortune.
The result came after only about 48 trillion numbers were tested when the same
**Manfred Toplic** found the winning *N*.

Newsletter/1 : 16 February 1998.

Newsletter/2 : 2 March 1998.

Newsletter/3 - the official announcement : 7 March 1998.

Ivars Peterson's report in *Math Trek* : 23 March 1998.

The paper : 28 November 2001.

Newsletter/1 : 9 November 1997.

Newsletter/2 : 23 November 1997.

Newsletter/3 : 6 December 1997.

Newsletter/4 : 23 December 1997.

Newsletter/5 : 15 January 1998.

Newsletter/6 : 24 January 1998.

Keith Devlin's
article in *The Guardian* : 19th February 1998.

Harvey Dubner and Harry Nelson, Seven primes in arithmetic progression,
*Mathematics of Computation*, October 1997. Also available as a
PDF file.

Harvey Dubner, Tony Forbes, Nik Lygeros, Michel Mizony and Paul Zimmermann,
8 consec. primes in AP,
*NMBRTHRY*,
November 1997.

Harvey Dubner, Tony Forbes, Nik Lygeros, Michel Mizony and Paul Zimmermann,
9 consecutive primes in arithmetic progression,
*NMBRTHRY*,
January 1998.

Harvey Dubner, Tony Forbes, Nik Lygeros, Michel Mizony, H. Nelson and Paul Zimmermann,
Ten consecutive primes in arithmetic progression,
*Mathematics of Computation* **71** (2002). Also available as a
PDF file.

Richard K. Guy, *Unsolved Problems in Number Theory*, Springer-Verlag,
1994, 2nd edition, Section A.6.

Ivars Peterson, A Progression of Primes,
*Ivars Peterson's MathTrek*, 17 November 1997.

Ivars Peterson, Nine Primes in a Row,
*Ivars Peterson's MathTrek*, 9 February 1998.

Ivars Peterson, A Prime Surprise,
*Ivars Peterson's MathTrek*, 23 March 1998.

Paulo Ribenboim, *The New Book of Prime Number Records*,
Springer-Verlag, 1995, 3rd edition, Section IV.C.