A101521 Indices of primes in sequence defined by A(0) = 69, A(n) = 10*A(n-1) - 71 for n > 0.

1, 259, 416, 952, 2137, 2968, 3044, 11776, 23647

Offset

1,2

Comments

Numbers n such that (550*10^n + 71)/9 is prime.

Numbers n such that digit 6 followed by n >= 0 occurrences of digit 1 followed by digit 9 is prime.

Numbers corresponding to terms <= 952 are certified primes.

a(10) > 10^5. - Robert Price, Sep 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..9.

Makoto Kamada, Prime numbers of the form 611...119.

Index entries for primes involving repunits.

Formula

a(n) = A103029(n) - 1.

Example

619 is prime, hence 1 is a term.

Mathematica

Select[Range[0, 10000], PrimeQ[(550*10^# + 71)/9] &] (* Robert Price, Sep 08 2015 *)

Prog

(PARI) a=69; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-71)
(PARI) for(n=0, 1000, if(isprime((550*10^n+71)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103029.

Sequence in context: A239655 A246243 A066129 * A207060 A037987 A185673

Adjacent sequences: A101518 A101519 A101520 * A101522 A101523 A101524

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004

Extensions

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

a(8)-a(9) from Kamada data by Ray Chandler, Apr 30 2015

Status

approved