OFFSET
1,3
COMMENTS
Numbers n such that (180*10^n - 63)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 9 followed by digit 3 is prime.
Numbers corresponding to terms <= 303 are certified primes.
a(20) > 10^5. - Robert Price, Nov 16 2014
a(22) > 2*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) = A102946(n) - 1. - Robert Price, Nov 16 2014
EXAMPLE
193 is prime, hence 1 is a term.
MAPLE
A102033:=n->`if`(isprime((180*10^n-63)/9), n, NULL): seq(A102033(n), n=0..10^3); # Wesley Ivan Hurt, Nov 16 2014
MATHEMATICA
Select[Range[0, 10^3], PrimeQ[(180*10^# - 63)/9] &] (* Wesley Ivan Hurt, Nov 16 2014 *)
PROG
(PARI) a=13; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+63)
(PARI) for(n=0, 1500, if(isprime((180*10^n-63)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(18)-a(19) derived from A102946 by Robert Price, Nov 16 2014
a(20)-a(21) from Robert Price, Oct 25 2015
STATUS
approved