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A101736
Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) + 17 for n > 0.
1
0, 1, 6, 13, 24, 115, 426, 594, 636, 775, 1705, 16627, 55557
OFFSET
1,3
COMMENTS
Numbers n such that (440*10^n - 17)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 8 followed by digit 7 is prime.
Numbers corresponding to terms <= 775 are certified primes.
a(14) > 10^5. - Robert Price, Jun 05 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102999(n) - 1.
EXAMPLE
487 is prime, hence 1 is a term.
MATHEMATICA
For[n=0, n<= 3000, n++, If[PrimeQ[(440*10^n - 17)/9], Print[n]]] (Steinerberger)
PROG
(PARI) a=47; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+17)
(PARI) for(n=0, 1500, if(isprime((440*10^n-17)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004
EXTENSIONS
a(11) from Stefan Steinerberger, Feb 04 2006
a(12) from Kamada data by Ray Chandler, May 01 2015
a(13) from Robert Price, Jun 05 2015
STATUS
approved