A101837 Indices of primes in sequence defined by A(0) = 37, A(n) = 10*A(n-1) - 13 for n > 0.

0, 2, 5, 11, 32, 68, 110, 1964, 5645, 7403, 11102, 20789, 24839, 38198, 90668

Offset

1,2

Comments

Numbers n such that (320*10^n + 13)/9 is prime.

Numbers n such that digit 3 followed by n >= 0 occurrences of digit 5 followed by digit 7 is prime.

a(16) > 10^5. - Robert Price, Apr 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..15.

Makoto Kamada, Prime numbers of the form 355...557.

Index entries for primes involving repunits.

Formula

a(n) = A102972(n+1) - 1.

Example

3557 is prime, hence 2 is a term.

Mathematica

Select[Range[0, 10000], PrimeQ[(320*10^# + 13)/9] &] (* Robert Price, Apr 07 2015 *)

Prog

(PARI) a=37; for(n=0, 2000, if(isprime(a), print1(n, ", ")); a=10*a-13)
(PARI) for(n=0, 2000, if(isprime((320*10^n+13)/9), print1(n, ", ")))
(Magma) [n: n in [0..1000] | IsPrime((320*10^n+13) div 9)]; // Vincenzo Librandi, Apr 08 2015

Crossrefs

Cf. A000533, A002275, A102972.

Sequence in context: A275427 A139464 A174537 * A124483 A079571 A151395

Adjacent sequences: A101834 A101835 A101836 * A101838 A101839 A101840

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(11)-a(15) derived from A102972 by Robert Price, Apr 07 2015

Status

approved