A185084 Number of Fermat pseudoprimes to base 3 less than 2^n.

0, 0, 0, 0, 0, 0, 2, 2, 3, 6, 10, 17, 21, 30, 44, 61, 87, 124, 175, 254, 362, 511, 696, 955, 1313, 1802, 2462, 3321, 4422, 5969, 8089, 10785, 14513, 19333, 25774, 34259, 45522

Offset: 1

Author

Washington Bomfim, Mar 02 2012

Keywords

• nonn
• more

Examples

			a(1) = a(2) = ... = a(6) = 0 because A005935(1) = 91 > 2^6.
a(7) = 2 since A005935(1) = 91, A005935(2) = 121, A005935(3) = 286, and 121 < 2^7 < 286.
		

Crossrefs

Cf. A005935, A114245.

Programs

Mathematica

cnt = 0; Table[Do[If[! PrimeQ[i] && PowerMod[3, i-1, i] == 1, cnt++], {i, 2^(n-1) + 1, 2^n}]; cnt, {n, 20}] (* T. D. Noe, Mar 02 2012 *)

Extensions

a(35)-a(37) from Amiram Eldar, Jul 18 2021