A101569 Indices of primes in sequence defined by A(0) = 59, A(n) = 10*A(n-1) - 81 for n > 0.

0, 1, 2, 4, 7, 19, 28, 85, 282, 756, 1198, 2472, 2732, 24852, 39628, 53491, 71236, 72301, 81652, 167509

Offset

1,3

Comments

Numbers n such that 50*10^n + 9 is prime.

Numbers n such that digit 5 followed by n >= 0 occurrences of digit 0 followed by digit 9 is prime.

Numbers corresponding to terms <= 756 are certified primes.

a(21) > 2*10^5. - Robert Price, Aug 10 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..20.

Makoto Kamada, Prime numbers of the form 500...009.

Formula

a(n) = A103004(n) - 1.

Example

500009 is prime, hence 4 is a term.

Mathematica

Select[Range[0, 200000], PrimeQ[50*10^# + 9] &] (* Robert Price, Aug 10 2015 *)

Prog

(PARI) a=59; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-81)
(PARI) for(n=0, 1500, if(isprime(50*10^n+9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103004.

Sequence in context: A223013 A276027 A367440 * A225435 A243049 A247234

Adjacent sequences: A101566 A101567 A101568 * A101570 A101571 A101572

Keyword

nonn,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(14)-a(19) from Kamada data by Ray Chandler, Apr 30 2015

a(20) from Robert Price, Aug 10 2015

Status

approved