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A101847 Indices of primes in sequence defined by A(0) = 39, A(n) = 10*A(n-1) - 1 for n > 0. 1
1, 2, 5, 16, 19, 44, 56, 77, 118, 136, 508, 709, 1126, 1517, 1760, 3085, 3146, 9925, 19853, 27841, 46798, 49681, 68717, 100541, 106648, 191072 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that (350*10^n + 1)/9 is prime.

Numbers n such that digit 3 followed by n >= 0 occurrences of digit 8 followed by digit 9 is prime.

Numbers corresponding to terms <= 709 are certified primes.

REFERENCES

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

LINKS

Table of n, a(n) for n=1..26.

Makoto Kamada, Prime numbers of the form 388...889.

Index entries for primes involving repunits.

FORMULA

a(n) = A102980(n) - 1.

EXAMPLE

3889 is prime, hence 2 is a term.

MATHEMATICA

Select[Range[0, 1000], PrimeQ[(350*10^# + 1)/9]&]

PROG

(PARI) a=39; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-1)

(PARI) for(n=0, 1500, if(isprime((350*10^n+1)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A102980.

Sequence in context: A127580 A098048 A257348 * A251600 A117557 A175735

Adjacent sequences:  A101844 A101845 A101846 * A101848 A101849 A101850

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(19)-a(26) derived from A102980 by Robert Price, Mar 17 2015

STATUS

approved

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Last modified June 26 10:12 EDT 2019. Contains 324375 sequences. (Running on oeis4.)