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A101002 Indices of primes in sequence defined by A(0) = 93, A(n) = 10*A(n-1) - 7 for n > 0. 1
4, 28, 59, 146, 185, 455, 677, 1372, 3377, 15725, 68230 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that (830*10^n + 7)/9 is prime.

Numbers n such that digit 9 followed by n >= 0 occurrences of digit 2 followed by digit 3 is prime.

Numbers corresponding to terms <= 677 are certified primes.

a(12) > 10^5. - Robert Price, Oct 31 2015

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..11.

Makoto Kamada, Prime numbers of the form 922...223.

Index entries for primes involving repunits.

FORMULA

a(n) = A103094(n) - 1.

EXAMPLE

922223 is prime, hence 4 is a term.

MATHEMATICA

Select[Range[0, 300], PrimeQ[(830*10^# + 7)/9] &] (* Robert Price, Oct 31 2015 *)

PROG

(PARI) a=93; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-7)

(PARI) for(n=0, 1500, if(isprime((830*10^n+7)/9 ), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A103094.

Sequence in context: A069518 A151912 A307135 * A197542 A203280 A085024

Adjacent sequences:  A100999 A101000 A101001 * A101003 A101004 A101005

KEYWORD

nonn,hard,more,less

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004

EXTENSIONS

One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(10) from Kamada data by Ray Chandler, Apr 28 2015

a(11) from Robert Price, Oct 31 2015

STATUS

approved

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Last modified October 22 01:48 EDT 2021. Contains 348160 sequences. (Running on oeis4.)