OFFSET
1,1
COMMENTS
Numbers n such that (860*10^n - 41)/9 is prime.
Numbers n such that digit 9 followed by n >= 0 occurrences of digit 5 followed by digit 1 is prime.
Numbers corresponding to terms <= 980 are certified primes.
a(24) > 10^5. - Robert Price, Nov 10 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A103100(n+1) - 1.
EXAMPLE
9551 is prime, hence 2 is a term.
MATHEMATICA
Flatten[Position[NestList[10#+41&, 91, 5200], _?PrimeQ]-1] (* Harvey P. Dale, Jun 28 2012 *)
Select[Range[0, 100000], PrimeQ[(860*10^# - 41)/9] &] (* Robert Price, Nov 10 2015 *)
PROG
(PARI) a=91; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+41)
(PARI) for(n=0, 1500, if(isprime((860*10^n-41)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more,less
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(18)-a(20) from Kamada data by Ray Chandler, Apr 28 2015
a(21)-a(23) from Robert Price, Nov 10 2015
STATUS
approved