A101843 Indices of primes in sequence defined by A(0) = 39, A(n) = 10*A(n-1) - 11 for n > 0.

1, 2, 4, 5, 19, 775, 1184, 3163, 4211, 10732, 21725, 38234

Offset

1,2

Comments

Numbers n such that (340*10^n + 11)/9 is prime.

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

Numbers corresponding to terms <= 775 are certified primes.

a(13) > 10^5. - Robert Price, May 08 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 377...779.

Index entries for primes involving repunits.

Formula

a(n) = A102977(n+1) - 1.

Example

3779 is prime, hence 2 is a term.

Mathematica

Select[Range[0, 300], PrimeQ[(340*10^# + 11)/9] &] (* Robert Price, May 08 2015 *)

Prog

(PARI) a=39; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-11)
(PARI) for(n=0, 1500, if(isprime((340*10^n+11)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102977.

Sequence in context: A065063 A276311 A056440 * A192117 A084592 A101587

Adjacent sequences: A101840 A101841 A101842 * A101844 A101845 A101846

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004

Extensions

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

a(10)-a(12) from Kamada data by Ray Chandler, May 01 2015

Status

approved