A102011 Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n-1) - 61 for n > 0.

0, 2, 5, 50, 56, 62, 149, 392, 419, 546, 42023, 43062, 101612, 107384

Offset

1,2

Comments

Numbers n such that (110*10^n + 61)/9 is prime.

Numbers n such that digit 1 followed by n >= 0 occurrences of digit 2 followed by digit 9 is prime.

Numbers corresponding to terms <= 546 are certified primes.

a(13) > 10^5. - Robert Price, Jan 17 2015

a(15) > 2*10^5. - Tyler Busby, Feb 01 2023

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..14.

Makoto Kamada, Prime numbers of the form 122...229.

Index entries for primes involving repunits.

Formula

a(n) = A102931(n) - 1.

Example

1222229 is prime, hence 5 is a term.

Prog

(PARI) a=19; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-61)
(PARI) for(n=0, 1500, if(isprime((110*10^n+61)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102931.

Sequence in context: A099658 A357246 A244014 * A328151 A208797 A004098

Adjacent sequences: A102008 A102009 A102010 * A102012 A102013 A102014

Keyword

nonn,hard,more

Author

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

Extensions

a(11)-a(12) derived from A102931 by Robert Price, Jan 17 2015

a(13)-a(14) from Tyler Busby, Jan 31 2023

Status

approved