A101128 Indices of primes in sequence defined by A(0) = 71, A(n) = 10*A(n-1) - 9 for n > 0.

0, 1, 2, 3, 4, 7, 8, 44, 135, 141, 157, 242, 922, 1234, 2195, 4649, 6118, 7323, 9542, 13493, 20309, 20359, 232919, 830864, 902707

Offset

1,3

Comments

Numbers n such that 70*10^n + 1 is prime.

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

Numbers corresponding to terms <= 922 are certified primes.

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 700...001.

Index entries for primes involving repunits.

Formula

a(n) = A056804(n) - 1.

Example

700001 is prime, hence 4 is a term.

Prog

(PARI) a=71; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-9)
(PARI) for(n=0, 1500, if(isprime(70*10^n+1), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A056804.

Sequence in context: A225211 A159554 A256606 * A182802 A172024 A285500

Adjacent sequences: A101125 A101126 A101127 * A101129 A101130 A101131

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004

Extensions

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

a(21)-a(25) from Kamada data by Ray Chandler, Apr 29 2015

Status

approved