A101142 Indices of primes in sequence defined by A(0) = 79, A(n) = 10*A(n-1) - 41 for n > 0.

0, 3, 6, 33, 81, 450, 771, 2553, 6249, 15136, 20073, 37377, 53067

Offset

1,2

Comments

Numbers n such that (670*10^n + 41)/9 is prime.

Numbers n such that digit 7 followed by n >= 0 occurrences of digit 4 followed by digit 9 is prime.

Numbers corresponding to terms <= 771 are certified primes.

a(14) > 10^5. - Robert Price, Sep 27 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..13.

Makoto Kamada, Prime numbers of the form 744...449.

Index entries for primes involving repunits.

Formula

a(n) = A103059(n) - 1.

Example

74449 is prime, hence 3 is a term.

Mathematica

Select[Range[0, 100000], PrimeQ[(670*10^# + 41)/9] &] (* Robert Price, Sep 27 2015 *)

Prog

(PARI) a=79; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-41)
(PARI) for(n=0, 1000, if(isprime((670*10^n+41)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103059.

Sequence in context: A192166 A297444 A184508 * A298679 A261885 A186750

Adjacent sequences: A101139 A101140 A101141 * A101143 A101144 A101145

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(10)-a(12) from Kamada data by Ray Chandler, Apr 30 2015

a(13) from Robert Price, Sep 27 2015

Status

approved