OFFSET
1,2
COMMENTS
Numbers n such that (160*10^n - 61)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 7 followed by digit 1 is prime.
Numbers corresponding to terms <= 1001 are certified primes.
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
Patrick De Geest, PDP Reference Table - 171.
Makoto Kamada, Prime numbers of the form 177...771.
FORMULA
a(n) = A082701(n-1) - 2 for n > 1.
EXAMPLE
1777771 is prime, hence 5 is a term.
MATHEMATICA
Flatten[Position[NestList[10#+61&, 11, 38000], _?PrimeQ]-1] (* Harvey P. Dale, Apr 17 2014 *)
Select[Range[0, 2000], PrimeQ[(160 10^# - 61) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)
PROG
(PARI) a=11; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+61)
(PARI) for(n=0, 1500, if(isprime((160*10^n-61)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
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 one more term from PDP table and a link. Updated comments section and a link, by Patrick De Geest, Nov 02 2014
Edited by Ray Chandler, Nov 04 2014
STATUS
approved