

A101521


Indices of primes in sequence defined by A(0) = 69, A(n) = 10*A(n1)  71 for n > 0.


1




OFFSET

1,2


COMMENTS

Numbers n such that (550*10^n + 71)/9 is prime.
Numbers n such that digit 6 followed by n >= 0 occurrences of digit 1 followed by digit 9 is prime.
Numbers corresponding to terms <= 952 are certified primes.
a(10) > 10^5.  Robert Price, Sep 08 2015


REFERENCES

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462467.


LINKS

Table of n, a(n) for n=1..9.
Makoto Kamada, Prime numbers of the form 611...119.
Index entries for primes involving repunits.


FORMULA

a(n) = A103029(n)  1.


EXAMPLE

619 is prime, hence 1 is a term.


MATHEMATICA

Select[Range[0, 10000], PrimeQ[(550*10^# + 71)/9] &] (* Robert Price, Sep 08 2015 *)


PROG

(PARI) a=69; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a71)
(PARI) for(n=0, 1000, if(isprime((550*10^n+71)/9), print1(n, ", ")))


CROSSREFS

Cf. A000533, A002275, A103029.
Sequence in context: A239655 A246243 A066129 * A207060 A037987 A185673
Adjacent sequences: A101518 A101519 A101520 * A101522 A101523 A101524


KEYWORD

nonn,hard,more


AUTHOR

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


EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(8)a(9) from Kamada data by Ray Chandler, Apr 30 2015


STATUS

approved



