A101014 Indices of primes in sequence defined by A(0) = 91, A(n) = 10*A(n-1) + 61 for n > 0.

1, 3, 40, 52, 63, 196, 237, 783, 3913, 4435, 12537, 19035

Offset

1,2

Comments

Numbers n such that (880*10^n - 61)/9 is prime.

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

Numbers corresponding to terms <= 783 are certified primes.

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

Makoto Kamada, Prime numbers of the form 977...771.

Index entries for primes involving repunits.

Formula

a(n) = A103105(n+1) - 1.

Example

97771 is prime, hence 3 is a term.

Mathematica

Select[Range[500], PrimeQ[(880*10^#-61)/9]&] (* Harvey P. Dale, Jul 19 2011 *)

Prog

(PARI) a=91; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+61)
(PARI) for(n=0, 1000, if(isprime((880*10^n-61)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103105.

Sequence in context: A084186 A037104 A100306 * A262036 A041347 A326608

Adjacent sequences: A101011 A101012 A101013 * A101015 A101016 A101017

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004

Extensions

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

a(11)-a(12) from Kamada data by Ray Chandler, Apr 28 2015

Status

approved