A297423 Numbers k such that (4*10^(2k) - 2*(10^k) + 1)/3 is prime.

1, 2, 97, 118, 223, 318, 350, 1369, 1590, 2658, 33295

Offset

1,2

Comments

Numbers of this form divide 8*(10^3k)+1.

a(11) > 3000. - Jon E. Schoenfield, Jan 01 2018

a(12) > 50000. - Robert Price, Apr 15 2018

Links

Table of n, a(n) for n=1..11.

Example

127 and 13267 are prime, while 1332667=7*61*3121, 133326667=19*937*7489, and 13333333266666667=6247609*2134149763.

Mathematica

Select[Range[1500], PrimeQ[(4 (10^(2 #)) - 2 (10^#) + 1)/3] &] (* Michael De Vlieger, Dec 30 2017 *)

Prog

(PARI) isok(k) = isprime((4*10^(2*k) - 2*(10^k) + 1)/3); \\ Michel Marcus, Dec 30 2017

Crossrefs

Sequence in context: A164335 A132206 A139884 * A189313 A042151 A233192

Adjacent sequences: A297420 A297421 A297422 * A297424 A297425 A297426

Keyword

nonn,more

Author

Patrick A. Thomas, Dec 30 2017

Extensions

a(3)-a(5) from Michel Marcus, Dec 30 2017

a(6)-a(9) from Michael De Vlieger, Dec 30 2017

a(10) from Jon E. Schoenfield, Jan 01 2018

a(11) from Robert Price, Apr 15 2018

Status

approved