A101571 Indices of primes in sequence defined by A(0) = 57, A(n) = 10*A(n-1) - 53 for n > 0.

22, 52, 12808, 15070

Offset

1,1

Comments

Numbers n such that (460*10^n + 53)/9 is prime.

Numbers n such that digit 5 followed by n >= 0 occurrences of digit 1 followed by digit 7 is prime.

Numbers corresponding to terms <= 52 are certified primes. No further terms up to 2400.

a(5) > 10^5. - Robert Price, Jun 20 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..4.

Makoto Kamada, Prime numbers of the form 511...117.

Index entries for primes involving repunits.

Formula

a(n) = A103006(n+1) - 1.

Example

511111111111111111111117 is prime, hence 22 is a term.

Prog

(PARI) a=57; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-53)
(PARI) for(n=0, 1000, if(isprime((460*10^n+53)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103006.

Sequence in context: A111576 A277979 A177726 * A290381 A324486 A351170

Adjacent sequences: A101568 A101569 A101570 * A101572 A101573 A101574

Keyword

nonn,more

Author

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

Extensions

a(3)-a(4) from Kamada data by Ray Chandler, Apr 30 2015

Status

approved