A101736 Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) + 17 for n > 0.

0, 1, 6, 13, 24, 115, 426, 594, 636, 775, 1705, 16627, 55557

Offset

1,3

Comments

Numbers n such that (440*10^n - 17)/9 is prime.

Numbers n such that digit 4 followed by n >= 0 occurrences of digit 8 followed by digit 7 is prime.

Numbers corresponding to terms <= 775 are certified primes.

a(14) > 10^5. - Robert Price, Jun 05 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 488...887.

Index entries for primes involving repunits.

Formula

a(n) = A102999(n) - 1.

Example

487 is prime, hence 1 is a term.

Mathematica

For[n=0, n<= 3000, n++, If[PrimeQ[(440*10^n - 17)/9], Print[n]]] (Steinerberger)

Prog

(PARI) a=47; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+17)
(PARI) for(n=0, 1500, if(isprime((440*10^n-17)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102999.

Sequence in context: A032528 A058535 A131833 * A162432 A117072 A081395

Adjacent sequences: A101733 A101734 A101735 * A101737 A101738 A101739

Keyword

nonn,hard

Author

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

Extensions

a(11) from Stefan Steinerberger, Feb 04 2006

a(12) from Kamada data by Ray Chandler, May 01 2015

a(13) from Robert Price, Jun 05 2015

Status

approved