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A101844
Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) + 71 for n > 0.
1
0, 2, 18, 29, 39, 41, 44, 69, 306, 537, 1608, 1667, 1673, 4491, 4934, 6111, 12818, 14078, 16019, 23004, 50996, 82869
OFFSET
1,2
Numbers n such that (350*10^n - 71)/9 is prime.
Numbers n such that digit 3 followed by n >= 0 occurrences of digit 8 followed by digit 1 is prime.
Numbers corresponding to terms <= 537 are certified primes.
a(23) > 10^5. - Robert Price, May 20 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102978(n) - 1.
EXAMPLE
3881 is prime, hence 2 is a term.
MATHEMATICA
#-1&/@(Flatten[Position[NestList[10#+71&, 31, 6200], _?(PrimeQ[#]&)]]) (* Harvey P. Dale, Aug 20 2011 *)
PROG
(PARI) a=31; for(n=0, 1700, if(isprime(a), print1(n, ", ")); a=10*a+71)
(PARI) for(n=0, 1700, if(isprime((350*10^n-71)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(17)-a(20) from Kamada data by Ray Chandler, May 01 2015
a(21)-a(22) from Robert Price, May 20 2015
STATUS
approved

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Last modified September 20 16:32 EDT 2024. Contains 376074 sequences. (Running on oeis4.)