A101522 Indices of primes in sequence defined by A(0) = 61, A(n) = 10*A(n-1) + 11 for n > 0.

0, 2, 6, 15, 38, 228, 351, 432, 765, 2886, 2975, 10835, 15096

Offset

1,2

Comments

Numbers n such that (560*10^n - 11)/9 is prime.

Numbers n such that digit 6 followed by n >= 0 occurrences of digit 2 followed by digit 1 is prime.

Numbers corresponding to terms <= 765 are certified primes.

a(14) > 10^5. - Robert Price, Sep 08 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..13.

Makoto Kamada, Prime numbers of the form 622...221.

Index entries for primes involving repunits.

Formula

a(n) = A103030(n+1) - 1.

Example

62222221 is prime, hence 6 is a term.

Mathematica

Select[Range[0, 100000], PrimeQ[(560*10^# - 11)/9] &] (* Robert Price, Sep 08 2015 *)

Prog

(PARI) a=61; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+11)
(PARI) for(n=0, 1000, if(isprime((560*10^n-11)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103030.

Sequence in context: A109545 A191634 A120846 * A094969 A001674 A121331

Adjacent sequences: A101519 A101520 A101521 * A101523 A101524 A101525

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004

Extensions

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

a(12)-a(13) from Kamada data by Ray Chandler, Apr 30 2015

Status

approved