A101962 Indices of primes in sequence defined by A(0) = 27, A(n) = 10*A(n-1) - 13 for n > 0.

1, 2, 25, 26, 44, 61, 146, 1276, 1664, 1978, 2969, 12772, 17701, 19127, 22205, 22385, 25052

Offset

1,2

Comments

Numbers n such that (230*10^n + 13)/9 is prime.

Numbers n such that digit 2 followed by n >= 0 occurrences of digit 5 followed by digit 7 is prime.

a(18) > 10^5. - Robert Price, Feb 16 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..17.

Makoto Kamada, Prime numbers of the form 255...557.

Index entries for primes involving repunits.

Formula

a(n) = A099006(n) - 1.

Example

2557 is prime, hence 2 is a term.

Prog

(PARI) a=27; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-13)
(PARI) for(n=0, 1500, if(isprime((230*10^n+13)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A099006.

Sequence in context: A036502 A076449 A153811 * A092045 A317886 A054283

Adjacent sequences: A101959 A101960 A101961 * A101963 A101964 A101965

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(12)-a(17) derived from A099006 by Robert Price, Feb 16 2015

Status

approved