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

1,2

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

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..10.

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

Formula

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

Example

200009 is prime, hence 4 is a term.

Mathematica

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

Prog

(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, ", ")))

Crossrefs

Cf. A000533, A002275, A101392.

Sequence in context: A296398 A166947 A103624 * A009535 A139096 A111425

Adjacent sequences: A101949 A101950 A101951 * A101953 A101954 A101955

Keyword

nonn,hard,more

Author

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

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

Status

approved