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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A101018 Indices of primes in sequence defined by A(0) = 97, A(n) = 10*A(n-1) + 17 for n > 0. 1
0, 2, 3, 5, 8, 11, 15, 33, 128, 242, 251, 528, 4884, 6362, 12950, 13187, 29930, 34887, 49515, 67430, 77780 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that (890*10^n - 17)/9 is prime.

Numbers n such that digit 9 followed by n >= 0 occurrences of digit 8 followed by digit 7 is prime.

Numbers corresponding to terms <= 528 are certified primes.

a(22) > 10^5. - Robert Price, Nov 14 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..21.

Makoto Kamada, Prime numbers of the form 988...887.

Index entries for primes involving repunits.

FORMULA

a(n) = A103109(n) - 1.

EXAMPLE

9888887 is prime, hence 5 is a term.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(890*10^# - 17)/9] &] (* Robert Price, Nov 14 2015 *)

PROG

(PARI) a=97; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+17)

(PARI) for(n=0, 1000, if(isprime((890*10^n-17)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A103109.

Sequence in context: A071424 A008762 A308823 * A320593 A006336 A175831

Adjacent sequences:  A101015 A101016 A101017 * A101019 A101020 A101021

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(15)-a(19) from Kamada data by Ray Chandler, Apr 29 2015

a(20)-a(21) from Robert Price, Nov 14 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 November 15 18:59 EST 2019. Contains 329149 sequences. (Running on oeis4.)