A101575 Indices of primes in sequence defined by A(0) = 57, A(n) = 10*A(n-1) - 43 for n > 0.

2, 4, 32, 47, 58, 59, 73, 125, 176, 227, 637, 1303, 1643, 2434, 4373, 8749, 15113, 16852, 30352, 30544, 36235

Offset

1,1

Comments

Numbers n such that (470*10^n + 43)/9 is prime.

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

Numbers corresponding to terms <= 637 are certified primes.

a(22) > 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..21.

Makoto Kamada, Prime numbers of the form 522...227.

Index entries for primes involving repunits.

Formula

a(n) = A103010(n) - 1.

Example

522227 is prime, hence 4 is a term.

Prog

(PARI) a=57; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-43)
(PARI) for(n=0, 1500, if(isprime((470*10^n+43)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103010.

Sequence in context: A319223 A299783 A293760 * A197099 A009098 A192387

Adjacent sequences: A101572 A101573 A101574 * A101576 A101577 A101578

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(21) from Kamada data by Ray Chandler, Apr 30 2015

Status

approved