A101952 Indices of primes in sequence defined by A(0) = 29, A(n) = 10*A(n-1) - 81 for n > 0.

0, 4, 24, 454, 760, 9204, 13560, 15954, 26668, 113940

Offset: 1

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004

Keywords

• nonn
• hard
• more

Comments

Numbers n such that 20*10^n + 9 is prime.

Numbers n such that digit 2 followed by n >= 0 occurrences of digit 0 followed by digit 9 is prime.

Numbers corresponding to terms <= 760 are certified primes.

a(11) > 2*10^5. - Robert Price, Jun 06 2015

Examples

			200009 is prime, hence 4 is a term.
		

References

• Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

Links

• Makoto Kamada, Prime numbers of the form 200...009.

Crossrefs

Cf. A000533, A002275, A101392.

Programs

Mathematica

Select[Range[0, 300], PrimeQ[20*10^# + 9] &] (* Robert Price, Jun 06 2015 *)

PARI

a=29;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-81)

PARI

for(n=0,1500,if(isprime(20*10^n+9),print1(n,",")))

Formula

a(n) = A101392(n-1) - 1. - Robert Price, Nov 25 2014

Extensions

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

a(9)-a(10) derived from A101392 by Robert Price, Nov 25 2014