login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Today, Nov 11 2014, is the 4th anniversary of the launch of the new OEIS web site. 70,000 sequences have been added in these four years, all edited by volunteers. Please make a donation (tax deductible in the US) to help keep the OEIS running.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A101016 Indices of primes in sequence defined by A(0) = 91, A(n) = 10*A(n-1) + 71 for n > 0. 0
5, 8, 89, 110, 209, 236, 413, 1191, 1259, 5835, 6771 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that (890*10^n - 71)/9 is prime.

Numbers n such that digit 9 followed by n >= 0 occurrences of digit 8 followed by digit 1 is prime.

Numbers corresponding to terms <= 413 are certified primes.

Certified primality of terms corresponding to 1191 and 1259 with Primo. - Ryan Propper, Jun 20 2005

Next term after 6771 is greater than 10000. - Ryan Propper, Jun 20 2005

REFERENCES

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

LINKS

Table of n, a(n) for n=1..11.

EXAMPLE

9888881 is prime, hence 5 is a term.

PROG

(PARI) a=91; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+71)

(PARI) for(n=0, 1500, if(isprime((890*10^n-71)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275.

a(n) = A103107(n) - 1.

Sequence in context: A213239 A123819 A153720 * A025518 A151827 A162571

Adjacent sequences:  A101013 A101014 A101015 * A101017 A101018 A101019

KEYWORD

nonn,hard,more

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004

EXTENSIONS

Two additional terms, corresponding to probable primes, from Ryan Propper, Jun 20 2005

Edited by T. D. Noe, Oct 30 2008

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified December 22 14:10 EST 2014. Contains 252364 sequences.