A101537 Indices of primes in sequence defined by A(0) = 61, A(n) = 10*A(n-1) + 71 for n > 0.

0, 3, 9, 12, 177, 303, 330, 501, 743, 1026, 1769, 5304, 55074

Offset

1,2

Comments

Numbers n such that (620*10^n - 71)/9 is prime.

Numbers n such that digit 6 followed by n >= 0 occurrences of digit 8 followed by digit 1 is prime.

Numbers corresponding to terms <= 743 are certified primes.

a(14) > 10^5. - Robert Price, Sep 15 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 688...881.

Index entries for primes involving repunits.

Formula

a(n) = A103044(n) - 1.

Example

68881 is prime, hence 3 is a term.

Mathematica

Select[Range[0, 100000], PrimeQ[(620*10^# - 71)/9] &] (* Robert Price, Sep 15 2015 *)

Prog

(PARI) a=61; for(n=0, 1200, if(isprime(a), print1(n, ", ")); a=10*a+71)
(PARI) for(n=0, 1200, if(isprime((620*10^n-71)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103044.

Sequence in context: A357726 A045769 A262539 * A070353 A029458 A050571

Adjacent sequences: A101534 A101535 A101536 * A101538 A101539 A101540

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(13) from Robert Price, Sep 15 2015

Status

approved