A265309 Numbers n such that (10^(n+4)*7 - 36763)/9 is prime (n > 0).

1, 2, 4, 7, 14, 17, 55, 61, 259, 269, 791, 3613, 6448, 8317, 18194, 32219

Offset

1,2

Comments

Numbers n such that '3693' appended to n times the digit 7 is prime. Up to a(15) nonprimes alternate with primes.

A(n) mod 3 -> {1, 2, 1, 1, 2, 2, 1, 1, 1, 2, 2, 1, 1, 1, 2, 2, ...?}.

Links

Table of n, a(n) for n=1..16.

Example

4 appears because 77773693 is prime ('7' concatenated 4 times and prepended to '3693') is prime).

Maple

A265309:= n->`if`(isprime((10^(n + 4) * 7 - 36763)/9), n, NULL):
seq(A265309(n), n=1..1000);

Mathematica

Select[ Range[10^3], PrimeQ[(10^(# + 4) * 7 - 36763)/9] &]

Prog

(Magma)[n: n in[1 .. 1000] | IsPrime((10^(n+4) * 7 - 36763) div 9)];
(PARI) is(n)=isprime((10^(n+4)*7 - 36763)/9)

Crossrefs

Cf. A260903.

Sequence in context: A222306 A248220 A018476 * A293825 A289050 A133638

Adjacent sequences: A265306 A265307 A265308 * A265310 A265311 A265312

Keyword

nonn,base,more

Author

Mikk Heidemaa, Dec 06 2015

Status

approved