A101831 Indices of primes in sequence defined by A(0) = 39, A(n) = 10*A(n-1) - 61 for n > 0.

2, 4, 8, 11, 26, 50, 52, 146, 154, 256, 518, 602, 2884, 9508, 10523, 19649, 32507, 79444

Offset

1,1

Comments

Numbers n such that (290*10^n + 61)/9 is prime.

Numbers n such that digit 3 followed by n >= 0 occurrences of digit 2 followed by digit 9 is prime.

a(19) > 10^5. - Robert Price, Apr 05 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..18.

Makoto Kamada, Prime numbers of the form 322...229.

Index entries for primes involving repunits.

Formula

a(n) = A102968(n) - 1.

Example

3229 is prime, hence 2 is a term.

Mathematica

Select[Range[0, 1000], PrimeQ[(290*10^# + 61)/9] &] (* Robert Price, Apr 05 2015 *)

Prog

(PARI) a=39; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-61)
(PARI) for(n=0, 1500, if(isprime((290*10^n+61)/9), print1(n, ", ")))
(Magma) [n: n in [0..500] | IsPrime((290*10^n+61) div 9)]; // Vincenzo Librandi, Apr 06 2015

Crossrefs

Cf. A000533, A002275, A102968.

Sequence in context: A018277 A004654 A018749 * A246703 A079389 A324991

Adjacent sequences: A101828 A101829 A101830 * A101832 A101833 A101834

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(15)-a(18) derived from A102968 by Robert Price, Apr 05 2015

Status

approved