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A101061 Indices of primes in sequence defined by A(0) = 81, A(n) = 10*A(n-1) + 11 for n > 0. 1
1, 2, 4, 16, 46, 176, 8461, 36614 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that (740*10^n - 11)/9 is prime.

Numbers n such that digit 8 followed by n >= 0 occurrences of digit 2 followed by digit 1 is prime.

Numbers corresponding to terms <= 176 are certified primes.

a(9) > 10^5. - Robert Price, Oct 13 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..8.

Makoto Kamada, Prime numbers of the form 822...221.

Index entries for primes involving repunits.

FORMULA

a(n) = A103074(n+1) - 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

EXAMPLE

822221 is prime, hence 4 is a term.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(740*10^# - 11)/9] &] (* Robert Price, Oct 13 2015 *)

PROG

(PARI) a=81; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+11)

(PARI) for(n=0, 1000, if(isprime((740*10^n-11)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A103074.

Sequence in context: A133465 A110128 A148279 * A148280 A112638 A077162

Adjacent sequences:  A101058 A101059 A101060 * A101062 A101063 A101064

KEYWORD

nonn,hard,more

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 30 2004

EXTENSIONS

8461 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(8) from Erik Branger May 01 2013 by Ray Chandler, Apr 29 2015

STATUS

approved

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Last modified August 15 00:20 EDT 2020. Contains 336484 sequences. (Running on oeis4.)