A101574 Indices of primes in sequence defined by A(0) = 53, A(n) = 10*A(n-1) - 7 for n > 0.

0, 1, 3, 6, 102, 165, 279, 474, 504, 834, 921, 2017, 4434, 4458, 7614, 8557, 17163, 22800

Offset

1,3

Comments

Numbers n such that (470*10^n + 7)/9 is prime.

Numbers n such that digit 5 followed by n >= 0 occurrences of digit 2 followed by digit 3 is prime.

Numbers corresponding to terms <= 921 are certified primes.

a(19) > 10^5. - Robert Price, Jul 10 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..18.

Makoto Kamada, Prime numbers of the form 522...223.

Index entries for primes involving repunits.

Formula

a(n) = A103009(n) - 1.

Example

52223 is prime, hence 3 is a term.

Prog

(PARI) a=53; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-7)
(PARI) for(n=0, 1500, if(isprime((470*10^n+7)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103009.

Sequence in context: A036286 A084008 A092680 * A082980 A157536 A046488

Adjacent sequences: A101571 A101572 A101573 * A101575 A101576 A101577

Keyword

nonn,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(17)-a(18) from Kamada data by Ray Chandler, Apr 30 2015

Status

approved