A101732 Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) + 61 for n > 0.

0, 21, 924, 2339, 15954, 16097, 55511, 82751

Offset

1,2

Comments

Numbers n such that (430*10^n - 61)/9 is prime.

Numbers n such that digit 4 followed by n >= 0 occurrences of digit 7 followed by digit 1 is prime.

Numbers corresponding to terms <= 924 are certified primes.

a(9) > 10^5. - Robert Price, Jun 01 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..8.

Makoto Kamada, Prime numbers of the form 477...771.

Index entries for primes involving repunits.

Formula

a(n) = A102995(n) - 1.

Example

47 is prime, hence 0 is a term.

Mathematica

Select[Range[0, 1000], PrimeQ[(430*10^# - 61)/9] &] (* Robert Price, Jun 01 2015 *)

Prog

(PARI) a=41; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+61)
(PARI) for(n=0, 1500, if(isprime((430*10^n-61)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102995.

Sequence in context: A041840 A012793 A015305 * A006301 A220384 A184133

Adjacent sequences: A101729 A101730 A101731 * A101733 A101734 A101735

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004

Extensions

a(5)-a(6) from Kamada data by Ray Chandler, May 01 2015

a(7)-a(8) from Robert Price, Jun 01 2015

Status

approved