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A101828
Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) + 11 for n > 0.
1
0, 2, 5, 11, 407, 648, 948, 962, 1004, 2699, 19778, 22517, 22610, 40583, 55361, 70193
OFFSET
1,2
COMMENTS
Numbers n such that (290*10^n - 11)/9 is prime.
Numbers n such that digit 3 followed by n >= 0 occurrences of digit 2 followed by digit 1 is prime.
Numbers corresponding to terms <= 962 are certified primes.
a(17) > 10^5. - Robert Price, Apr 04 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102966(n+1) - 1.
EXAMPLE
3221 is prime, hence 2 is a term.
MATHEMATICA
Select[Range[0, 1000], PrimeQ[(290*10^# - 11)/9] &](* Robert Price, Apr 04 2015 *)
PROG
(PARI) a=31; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+11)
(PARI) for(n=0, 1500, if(isprime((290*10^n-11)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
EXTENSIONS
2699 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(11)-a(16) derived from A102966 by Robert Price, Apr 04 2015
STATUS
approved