

A102008


Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n1)  81 for n > 0.


1



0, 1, 2, 3, 8, 17, 21, 44, 48, 55, 68, 145, 201, 271, 2729, 2840, 4561, 31809, 43185, 48108, 92690
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OFFSET

1,3


COMMENTS

Numbers n such that 10*10^n + 9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 0 followed by digit 9 is prime.
Numbers corresponding to terms <= 271 are certified primes.


REFERENCES

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


LINKS



FORMULA



EXAMPLE

1009 is prime, hence 2 is a term.


MATHEMATICA

Select[Range[0, 200000], PrimeQ[10*10^# + 9] &] (* Robert Price, Oct 11 2015 *)


PROG

(PARI) a=19; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a81)
(PARI) for(n=0, 1500, if(isprime(10*10^n + 9), print1(n, ", ")))


CROSSREFS



KEYWORD

nonn,hard,more


AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwthaachen.de), Dec 28 2004


EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008


STATUS

approved



