login
A101520
Indices of primes in sequence defined by A(0) = 67, A(n) = 10*A(n-1) - 53 for n > 0.
1
0, 1, 31, 42, 972, 1194, 4470, 5683, 7987, 46884
OFFSET
1,3
COMMENTS
Numbers n such that (550*10^n + 53)/9 is prime.
Numbers n such that digit 6 followed by n >= 0 occurrences of digit 1 followed by digit 7 is prime.
Numbers corresponding to terms <= 972 are certified primes.
a(11) > 10^5. - Robert Price, Sep 07 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103028(n) - 1.
EXAMPLE
67 is prime, hence 0 is a term.
MATHEMATICA
Select[Range[0, 10000], PrimeQ[(550*10^# + 53)/9] &] (* Robert Price, Sep 07 2015 *)
PROG
(PARI) a=67; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-53)
(PARI) for(n=0, 1500, if(isprime((550*10^n+53)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(10) from Erik Branger May 01 2013 by Ray Chandler, Apr 30 2015
STATUS
approved