A102028 Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n-1) - 11 for n > 0.

0, 1, 7, 9, 24, 49, 75, 103, 4405, 8934, 25999, 31651

Offset

1,3

Comments

Numbers n such that (160*10^n + 11)/9 is prime.

Numbers n such that digit 1 followed by n >= 0 occurrences of digit 7 followed by digit 9 is prime.

Numbers corresponding to terms <= 103 are certified primes.

a(13) > 10^5. - Robert Price, Feb 07 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..12.

Makoto Kamada, Prime numbers of the form 177...779.

Index entries for primes involving repunits.

Formula

a(n) = A102943(n) - 1.

Example

179 is prime, hence 1 is a term.

Prog

(PARI) a=19; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-11)
(PARI) for(n=0, 1500, if(isprime((160*10^n+11)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102943.

Sequence in context: A303188 A029633 A049301 * A265990 A125260 A192859

Adjacent sequences: A102025 A102026 A102027 * A102029 A102030 A102031

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

a(11)-a(12) derived from A102943 by Robert Price, Feb 07 2015

Status

approved