A101963 Indices of primes in sequence defined by A(0) = 29, A(n) = 10*A(n-1) - 31 for n > 0.

0, 81, 321, 732, 2430, 8385, 15885, 19911

Offset

1,2

Comments

Numbers n such that (230*10^n + 31)/9 is prime.

Numbers n such that digit 2 followed by n >= 0 occurrences of digit 5 followed by digit 9 is prime.

Numbers corresponding to terms <= 732 are certified primes.

a(9) > 10^5. - Robert Price, Feb 06 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 255...559.

Index entries for primes involving repunits.

Formula

a(n) = A102956(n) - 1.

Example

29 is prime, hence 0 is a term.

Prog

(PARI) a=29; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-31)
(PARI) for(n=0, 1500, if(isprime((230*10^n+31)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102956.

Sequence in context: A237332 A237325 A158776 * A053171 A237412 A237405

Adjacent sequences: A101960 A101961 A101962 * A101964 A101965 A101966

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(7)-a(8) derived from A102956 by Robert Price, Feb 06 2015

Status

approved