A101971 Indices of primes in sequence defined by A(0) = 27, A(n) = 10*A(n-1) + 17 for n > 0.

2, 5, 17, 68, 442, 448, 454, 2458, 4744, 7972, 14248, 31709

Offset

1,1

Comments

Numbers n such that (260*10^n - 17)/9 is prime.

Numbers n such that digit 2 followed by n >= 0 occurrences of digit 8 followed by digit 7 is prime.

Numbers corresponding to terms <= 454 are certified primes.

a(13) > 10^5. - Robert Price, Mar 28 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 288...887.

Index entries for primes involving repunits.

Formula

a(n) = A102962(n) - 1.

Example

2887 is prime, hence 2 is a term.

Mathematica

Select[Range@ 1000, PrimeQ[(260*10^# - 17)/9] &] (* Michael De Vlieger, Mar 29 2015 *)

Prog

(PARI) a=27; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+17)
(PARI) for(n=0, 1500, if(isprime((260*10^n-17)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102962.

Sequence in context: A056098 A239201 A027361 * A211387 A372376 A303952

Adjacent sequences: A101968 A101969 A101970 * A101972 A101973 A101974

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

a(11)-a(12) derived from A102962 by Robert Price, Mar 28 2015

Status

approved