A101584 Indices of primes in sequence defined by A(0) = 51, A(n) = 10*A(n-1) + 61 for n > 0.

1, 5, 8, 26, 29, 47, 140, 149, 371, 421, 1096, 3569, 4606, 5288, 10733, 11549, 32603, 42469, 46310, 67577

Offset

1,2

Comments

Numbers n such that (520*10^n - 61)/9 is prime.

Numbers n such that digit 5 followed by n >= 0 occurrences of digit 7 followed by digit 1 is prime.

Numbers corresponding to terms <= 421 are certified primes.

a(21) > 10^5. - Robert Price, Sep 05 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..20.

Makoto Kamada, Prime numbers of the form 577...771.

Index entries for primes involving repunits.

Formula

a(n) = A103019(n) - 1.

Example

571 is prime, hence 1 is a term.

Mathematica

Select[Range[0, 300], PrimeQ[(520*10^# - 61)/9] &] (* Robert Price, Sep 05 2015 *)

Prog

(PARI) a=51; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+61)
(PARI) for(n=0, 1500, if(isprime((520*10^n-61)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103019.

Sequence in context: A069959 A038250 A067973 * A112577 A192920 A162562

Adjacent sequences: A101581 A101582 A101583 * A101585 A101586 A101587

Keyword

nonn,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004

Extensions

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

a(15)-a(19) from Kamada data by Ray Chandler, Apr 30 2015

a(20) from Robert Price, Sep 05 2015

Status

approved