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

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A101015 Indices of primes in sequence defined by A(0) = 93, A(n) = 10*A(n-1) + 43 for n > 0. 1
5, 14, 35, 44, 446, 1030, 1238, 3491, 6068, 13646, 17237, 56270, 72710, 75380 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that (880*10^n - 43)/9 is prime.

Numbers n such that digit 9 followed by n >= 0 occurrences of digit 7 followed by digit 3 is prime.

Numbers corresponding to terms <= 1030 are certified primes.

a(15) > 10^5. - Robert Price, Nov 12 2015

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..14.

Makoto Kamada, Prime numbers of the form 977...773.

Index entries for primes involving repunits.

FORMULA

a(n) = A103106(n+1) - 1.

EXAMPLE

9777773 is prime, hence 5 is a term.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(880*10^# - 43)/9] &] (* Robert Price, Nov 12 2015 *)

PROG

(PARI) a=93; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+43)

(PARI) for(n=0, 1500, if(isprime((880*10^n-43)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A103106.

Sequence in context: A023515 A047860 A083332 * A076858 A001215 A066767

Adjacent sequences:  A101012 A101013 A101014 * A101016 A101017 A101018

KEYWORD

nonn,hard,more

AUTHOR

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

EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(10)-a(11) from Kamada data by Ray Chandler, Apr 29 2015

a(12)-a(14) from Robert Price, Nov 12 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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 14 01:22 EST 2019. Contains 329978 sequences. (Running on oeis4.)