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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A101540 Indices of primes in sequence defined by A(0) = 69, A(n) = 10*A(n-1) - 1 for n > 0. 1
4, 56, 500, 514, 626, 640, 724, 53110, 65330, 109672 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that (620*10^n + 1)/9 is prime.

Numbers n such that digit 6 followed by n >= 0 occurrences of digit 8 followed by digit 9 is prime.

Numbers corresponding to terms <= 724 are certified primes.

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..10.

Makoto Kamada, Prime numbers of the form 688...889.

Index entries for primes involving repunits.

FORMULA

a(n) = A103047(n) - 1.

EXAMPLE

688889 is prime, hence 4 is a term.

PROG

(PARI) a=69; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-1)

(PARI) for(n=0, 1000, if(isprime((620*10^n+1)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A103047.

Sequence in context: A204108 A077122 A020540 * A224181 A026740 A191466

Adjacent sequences:  A101537 A101538 A101539 * A101541 A101542 A101543

KEYWORD

nonn,hard,more

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004

EXTENSIONS

a(8)-a(10) from Kamada data by Ray Chandler, Apr 30 2015

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy .

Last modified June 21 21:27 EDT 2018. Contains 305644 sequences. (Running on oeis4.)