A101133 Indices of primes in sequence defined by A(0) = 71, A(n) = 10*A(n-1) + 11 for n > 0.

0, 3, 15, 24, 28, 40, 46, 87, 1131, 1569, 3984, 10608, 12174, 29368

Offset

1,2

Comments

Numbers n such that (650*10^n - 11)/9 is prime.

Numbers n such that digit 7 followed by n >= 0 occurrences of digit 2 followed by digit 1 is prime.

Some of the larger entries may only correspond to probable primes.

a(15) > 10^5. - Robert Price, Sep 23 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..14.

Makoto Kamada, Prime numbers of the form 722...221.

Index entries for primes involving repunits.

Formula

a(n) = A103052(n) - 1.

Example

72221 is prime, hence 3 is a term.

Mathematica

Select[Range[0, 100000], PrimeQ[(650*10^# - 11)/9] &] (* Robert Price, Sep 23 2015 *)

Prog

(PARI) a=71; for(n=0, 1200, if(isprime(a), print1(n, ", ")); a=10*a+11)
(PARI) for(n=0, 1200, if(isprime((650*10^n-11)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103052.

Sequence in context: A009210 A142882 A161467 * A061386 A366209 A365412

Adjacent sequences: A101130 A101131 A101132 * A101134 A101135 A101136

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004

Extensions

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

a(12)-a(14) from Kamada data by Ray Chandler, Apr 29 2015

Status

approved