A101143 Indices of primes in sequence defined by A(0) = 71, A(n) = 10*A(n-1) + 41 for n > 0.

0, 1, 4, 6, 22, 31, 37, 46, 115, 139, 228, 246, 733, 930, 1345, 2161, 2545, 6979, 10282, 10542, 12127, 13740, 105319

Offset

1,3

Comments

Numbers n such that (680*10^n - 41)/9 is prime.

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

Numbers corresponding to terms <= 930 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..23.

Makoto Kamada, Prime numbers of the form 755...551.

Index entries for primes involving repunits.

Formula

a(n) = A103060(n) - 1.

Example

751 is prime, hence 1 is a term.

Prog

(PARI) a=71; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+41)
(PARI) for(n=0, 1500, if(isprime((680*10^n-41)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103060.

Sequence in context: A088228 A272309 A108636 * A083157 A192154 A289385

Adjacent sequences: A101140 A101141 A101142 * A101144 A101145 A101146

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(19)-a(22) from Robert Price, Sep 27 2013

a(23) from Robert Price, Oct 13 2013

Status

approved