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A101001 Indices of primes in sequence defined by A(0) = 91, A(n) = 10*A(n-1) + 11 for n > 0. 1
2, 3, 23, 38, 62, 75, 107, 165, 519, 1809, 2348, 2561, 5783, 6447, 11691, 16035, 17553 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that (830*10^n - 11)/9 is prime.

Numbers n such that digit 9 followed by n >= 0 occurrences of digit 2 followed by digit 1 is prime.

Numbers corresponding to terms <= 519 are certified primes.

a(18) > 10^5. - Robert Price, Nov 03 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..17.

Makoto Kamada, Prime numbers of the form 922...221.

Index entries for primes involving repunits.

FORMULA

a(n) = A103093(n) - 1.

EXAMPLE

92221 is prime, hence 3 is a term.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(830*10^# - 11)/9] &] (* Robert Price, Nov 03 2015 *)

PROG

(PARI) a=91; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+11)

(PARI) for(n=0, 1000, if(isprime((830*10^n-11)/9 ), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A103093.

Sequence in context: A024773 A176892 A109615 * A231477 A215325 A215353

Adjacent sequences:  A100998 A100999 A101000 * A101002 A101003 A101004

KEYWORD

nonn,hard,more,less

AUTHOR

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

EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(15)-a(17) from Kamada data by Ray Chandler, Apr 28 2015

STATUS

approved

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Last modified August 5 10:01 EDT 2021. Contains 346464 sequences. (Running on oeis4.)