A101827 Indices of primes in sequence defined by A(0) = 39, A(n) = 10*A(n-1) - 71 for n > 0.

2, 142, 796, 3142, 18790, 20762, 96742

Offset

1,1

Comments

Numbers n such that (280*10^n + 71)/9 is prime.

Numbers n such that digit 3 followed by n >= 0 occurrences of digit 1 followed by digit 9 is prime.

Numbers corresponding to terms <= 796 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..7.

Makoto Kamada, Prime numbers of the form 311...119.

Index entries for primes involving repunits.

Formula

a(n) = A102965(n+1) - 1.

Example

3119 is prime, hence 2 is a term.

Prog

(PARI) a=39; for(n=0, 3200, if(isprime(a), print1(n, ", ")); a=10*a-71)
(PARI) for(n=0, 3200, if(isprime((280*10^n+71)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102965.

Sequence in context: A115890 A356747 A215187 * A283097 A371588 A304582

Adjacent sequences: A101824 A101825 A101826 * A101828 A101829 A101830

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004

Extensions

a(5)-a(7) derived from A102965 by Robert Price, Jan 26 2015

Status

approved