A101010 Indices of primes in sequence defined by A(0) = 93, A(n) = 10*A(n-1) + 23 for n > 0.

1, 19, 103, 328, 1441, 1720, 24886

Offset

1,2

Comments

Numbers n such that (860*10^n - 23)/9 is prime.

Numbers n such that digit 9 followed by n >= 0 occurrences of digit 5 followed by digit 3 is prime.

Numbers corresponding to terms <= 328 are certified primes.

a(8) > 10^5. - Robert Price, Nov 08 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..7.

Makoto Kamada, Prime numbers of the form 955...553.

Index entries for primes involving repunits.

Formula

a(n) = A103101(n+1) - 1.

Example

953 is prime, hence 1 is a term.

Mathematica

Select[Range[0, 100000], PrimeQ[(860*10^# - 23)/9] &] (* Robert Price, Nov 08 2015 *)

Prog

(PARI) a=93; for(n=0, 2000, if(isprime(a), print1(n, ", ")); a=10*a+23)
(PARI) for(n=0, 2000, if(isprime((860*10^n-23)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103101.

Sequence in context: A054658 A023296 A139948 * A356126 A201854 A195460

Adjacent sequences: A101007 A101008 A101009 * A101011 A101012 A101013

Keyword

nonn,hard,more

Author

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

Extensions

a(7) from Kamada data by Ray Chandler, Apr 28 2015

Status

approved