A101965 Indices of primes in sequence defined by A(0) = 29, A(n) = 10*A(n-1) - 21 for n > 0.

0, 1, 3, 6, 13, 19, 38, 101, 155, 456, 1189, 2307, 5869, 8313, 9702, 12827, 14958, 17994, 19729, 26479, 31439

Offset

1,3

Comments

Numbers n such that (240*10^n + 21)/9 is prime.

Numbers n such that digit 2 followed by n >= 0 occurrences of digit 6 followed by digit 9 is prime.

Numbers corresponding to terms <= 456 are certified primes.

a(22) > 10^5. - Robert Price, Jan 29 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..21.

Makoto Kamada, Prime numbers of the form 266...669.

Index entries for primes involving repunits.

Formula

a(n) = A102957(n+1) - 1.

Example

26669 is prime, hence 3 is a term.

Prog

(PARI) a=29; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-21)
(PARI) for(n=0, 1500, if(isprime((240*10^n+21)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102957.

Sequence in context: A080554 A259583 A064349 * A230370 A285246 A147009

Adjacent sequences: A101962 A101963 A101964 * A101966 A101967 A101968

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(16)-a(21) derived from A102957 by Robert Price, Jan 29 2015

Status

approved