OFFSET
1,3
COMMENTS
Numbers n such that (140*10^n + 13)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 5 followed by digit 7 is prime.
Numbers corresponding to terms <= 396 are certified primes.
a(15) > 10^5. - Robert Price, Jan 17 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A102937(n+1) - 1.
EXAMPLE
157 is prime, hence 1 is a term.
PROG
(PARI) a=17; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-13)
(PARI) for(n=0, 1500, if(isprime((140*10^n+13)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
EXTENSIONS
7590 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(12)-a(14) derived from A102937 by Robert Price, Jan 17 2015
STATUS
approved