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A101008
Indices of primes in sequence defined by A(0) = 97, A(n) = 10*A(n-1) - 23 for n > 0.
1
0, 1, 3, 24, 57, 147, 372, 420, 1914, 3745, 16783, 30049, 60025, 93345
OFFSET
1,3
COMMENTS
Numbers n such that (850*10^n + 23)/9 is a prime.
Numbers n such that digit 9 followed by n >= 0 occurrences of digit 4 followed by digit 7 is a prime.
Numbers corresponding to terms <= 420 are certified primes.
a(15) > 10^5. - Robert Price, Nov 14 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103099(n) - 1.
EXAMPLE
94447 is a prime, hence 3 is a term.
MATHEMATICA
Flatten[Position[NestList[10#-23&, 97, 3800], _?PrimeQ]]-1 (* Harvey P. Dale, Apr 05 2015 *)
Select[Range[0, 100000], PrimeQ[(850*10^# + 23)/9] &] (* Robert Price, Nov 14 2015 *)
PROG
(PARI) a=97; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-23)
(PARI) for(n=0, 1000, if(isprime((850*10^n + 23)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more,less
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(11)-a(12) from Kamada data by Ray Chandler, Apr 28 2015
a(13)-a(14) from Robert Price, Nov 14 2015
STATUS
approved