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A101963
Indices of primes in sequence defined by A(0) = 29, A(n) = 10*A(n-1) - 31 for n > 0.
1
0, 81, 321, 732, 2430, 8385, 15885, 19911
OFFSET
1,2
COMMENTS
Numbers n such that (230*10^n + 31)/9 is prime.
Numbers n such that digit 2 followed by n >= 0 occurrences of digit 5 followed by digit 9 is prime.
Numbers corresponding to terms <= 732 are certified primes.
a(9) > 10^5. - Robert Price, Feb 06 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102956(n) - 1.
EXAMPLE
29 is prime, hence 0 is a term.
PROG
(PARI) a=29; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-31)
(PARI) for(n=0, 1500, if(isprime((230*10^n+31)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(7)-a(8) derived from A102956 by Robert Price, Feb 06 2015
STATUS
approved