A101714 Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) - 63 for n > 0.

0, 2, 8, 38, 2322

Offset

1,2

Comments

Numbers n such that 40*10^n + 7 is prime.

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

Some of the larger entries may only correspond to probable primes.

a(6) > 2*10^5. - Robert Price May 16 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..5.

Makoto Kamada, Prime numbers of the form 400...007.

Formula

a(n) = A101395(n+1) - 1.

Example

4007 is prime, hence 2 is a term.

Mathematica

Select[Range[0, 3000], PrimeQ[40*10^# + 7] &] (* Robert Price, May 16 2015 *)

Prog

(PARI) a=47; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-63)
(PARI) for(n=0, 1500, if(isprime(40*10^n+7), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A101395.

Sequence in context: A198049 A198092 A207162 * A077318 A082014 A154133

Adjacent sequences: A101711 A101712 A101713 * A101715 A101716 A101717

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004

Status

approved