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A101732
Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) + 61 for n > 0.
1
0, 21, 924, 2339, 15954, 16097, 55511, 82751
OFFSET
1,2
COMMENTS
Numbers n such that (430*10^n - 61)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 7 followed by digit 1 is prime.
Numbers corresponding to terms <= 924 are certified primes.
a(9) > 10^5. - Robert Price, Jun 01 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102995(n) - 1.
EXAMPLE
47 is prime, hence 0 is a term.
MATHEMATICA
Select[Range[0, 1000], PrimeQ[(430*10^# - 61)/9] &] (* Robert Price, Jun 01 2015 *)
PROG
(PARI) a=41; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+61)
(PARI) for(n=0, 1500, if(isprime((430*10^n-61)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004
EXTENSIONS
a(5)-a(6) from Kamada data by Ray Chandler, May 01 2015
a(7)-a(8) from Robert Price, Jun 01 2015
STATUS
approved