A101018 Indices of primes in sequence defined by A(0) = 97, A(n) = 10*A(n-1) + 17 for n > 0.

0, 2, 3, 5, 8, 11, 15, 33, 128, 242, 251, 528, 4884, 6362, 12950, 13187, 29930, 34887, 49515, 67430, 77780

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: A008762 A308823 A363047 * 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