A056246 Indices of primes in sequence defined by A(0) = 11, A(n) = 10*A(n-1) + 41 for n > 0.

0, 1, 3, 19, 31, 399, 561, 7015, 37683

Offset

1,3

Comments

Numbers n such that (140*10^n - 41)/9 is a prime.

Numbers n such that digit 1 followed by n >= 0 occurrences of digit 5 followed by digit 1 is a prime.

Numbers corresponding to terms <= 561 are certified primes.

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.

Patrick De Geest, PDP Reference Table - 151.

Makoto Kamada, Prime numbers of the form 155...551.

Index entries for primes involving repunits.

Formula

a(n) = A082699(n-1) - 2 for n > 1.

Example

151 is a prime, hence 1 is a term.

Mathematica

Select[Range[0, 2000], PrimeQ[(140 10^# - 41) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)

Prog

(PARI) a=11; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+41)
(PARI) for(n=0, 1500, if(isprime((140*10^n-41)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A068646, A082699.

Sequence in context: A269414 A162307 A128069 * A360081 A061427 A069516

Adjacent sequences: A056243 A056244 A056245 * A056247 A056248 A056249

Keyword

nonn,hard

Author

Robert G. Wilson v, Aug 18 2000

Extensions

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

Edited by N. J. A. Sloane, Jun 15 2007

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

Added and updated a link, by Patrick De Geest, Nov 02 2014

Edited by Ray Chandler, Nov 04 2014

Status

approved