OFFSET
1,2
COMMENTS
Numbers n such that (140*10^n - 23)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 5 followed by digit 3 is prime.
Numbers corresponding to terms <= 75 are certified primes.
a(9) > 10^5. - Robert Price, Apr 10 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A102936(n) - 1.
EXAMPLE
1553 is prime, hence 2 is a term.
MATHEMATICA
Flatten[Position[NestList[10#+23&, 13, 75], _?PrimeQ]]-1 (* Harvey P. Dale, Jul 21 2013 *)
Select[Range[0, 10000], PrimeQ[(140*10^# - 23)/9] &] (* _Robert Price, Apr 10 2015 *)
PROG
(PARI) a=13; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+23)
(PARI) for(n=0, 1500, if(isprime((140*10^n-23)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
EXTENSIONS
a(7)-a(8) derived from A102936 by Robert Price, Apr 10 2015
STATUS
approved