

A101395


Numbers n such that 4*10^n+7 is prime.


1




OFFSET

1,3


COMMENTS

No further terms < 50000.
a(7) > 2*10^5.  Robert Price May 16 2015


LINKS

Table of n, a(n) for n=1..6.
Makoto Kamada, Prime numbers of the form 400...007.
Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.
Index entries for primes involving repunits.


FORMULA

a(n) = A101714(n1) + 1.


EXAMPLE

n = 1, 3, 9 are members since 47, 4007 and 4000000007 are primes.


MATHEMATICA

Do[ If[ PrimeQ[4*10^n + 7], Print[n]], {n, 0, 10000}]


PROG

(PARI) is(n)=ispseudoprime(4*10^n+7) \\ Charles R Greathouse IV, Jun 12 2017


CROSSREFS

Cf. A056806, A100501, A088274, A101714.
Sequence in context: A090012 A079096 A143293 * A229244 A218504 A292909
Adjacent sequences: A101392 A101393 A101394 * A101396 A101397 A101398


KEYWORD

hard,nonn


AUTHOR

Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005


STATUS

approved



