OFFSET
1,3
COMMENTS
Numbers n such that (780*10^n - 33)/9 is prime.
Numbers n such that digit 8 followed by n >= 0 occurrences of digit 6 followed by digit 3 is prime.
Numbers corresponding to terms <= 878 are certified primes.
a(26) > 10^5. - Robert Price, Oct 25 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A103087(n+1) - 1.
EXAMPLE
8663 is prime, hence 2 is a term.
MATHEMATICA
Flatten[Position[NestList[10#+33&, 83, 1000], _?PrimeQ]-1] (* To generate terms larger than 1000, increase the final constant in NestList. *) (* Harvey P. Dale, Oct 02 2012 *)
Select[Range[0, 100000], PrimeQ[(780*10^# - 33)/9] &] (* Robert Price, Oct 25 2015 *)
PROG
(PARI) a=83; for(n=0, 1200, if(isprime(a), print1(n, ", ")); a=10*a+33)
(PARI) for(n=0, 1200, if(isprime((780*10^n-33)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 30 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(20)-a(25) from Kamada data by Ray Chandler, Apr 29 2015
STATUS
approved