A102016 Indices of primes in sequence defined by A(0) = 17, A(n) = 10*A(n-1) - 23 for n > 0.

0, 2, 3, 5, 8, 21, 27, 33, 36, 60, 81, 273, 275, 734, 1442, 2214, 2967, 3300, 3882, 3990, 5151, 8031, 8945, 46641, 57690

Offset

1,2

Comments

Numbers n such that (130*10^n + 23)/9 is prime.

Numbers n such that digit 1 followed by n >= 0 occurrences of digit 4 followed by digit 7 is prime.

Numbers corresponding to terms <= 734 are certified primes.

a(26) > 10^5. - Robert Price, Feb 19 2015

a(26) > 2*10^5. - Tyler Busby, Feb 01 2023

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..25.

Makoto Kamada, Prime numbers of the form 144...447.

Index entries for primes involving repunits.

Formula

a(n) = A102934(n) - 1.

Example

1447 is prime, hence 2 is a term.

Prog

(PARI) a=17; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-23)
(PARI) for(n=0, 1500, if(isprime((130*10^n+23)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102934.

Sequence in context: A334535 A135568 A103004 * A002363 A041457 A161468

Adjacent sequences: A102013 A102014 A102015 * A102017 A102018 A102019

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

a(24)-a(25) derived from A102934 by Robert Price, Feb 19 2015

Status

approved