A101132 Indices of primes in sequence defined by A(0) = 79, A(n) = 10*A(n-1) - 71 for n > 0.

0, 1, 3, 16, 24, 31, 49, 73, 172, 1723, 2083, 11397

Offset

1,3

Comments

Numbers n such that (640*10^n + 71)/9 is prime.

Numbers n such that digit 7 followed by n >= 0 occurrences of digit 1 followed by digit 9 is prime.

Numbers corresponding to terms <= 172 are certified primes.

a(13) > 10^5. - Robert Price, Sep 21 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..12.

Makoto Kamada, Prime numbers of the form 711...119.

Index entries for primes involving repunits.

Formula

a(n) = A103051(n) - 1.

Example

71119 is prime, hence 3 is a term.

Mathematica

Select[Range[0, 100000], PrimeQ[(640*10^# + 71)/9] &] (* Robert Price, Sep 21 2015 *)

Prog

(PARI) a=79; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-71)
(PARI) for(n=0, 1000, if(isprime((640*10^n+71)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103051.

Sequence in context: A028687 A201274 A375711 * A153723 A091273 A256931

Adjacent sequences: A101129 A101130 A101131 * A101133 A101134 A101135

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004

Extensions

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

a(12) from Kamada data by Ray Chandler, Apr 29 2015

Status

approved