A255746 Squarefree semiprimes n such that n+4 is also a squarefree semiprime.

6, 10, 22, 34, 35, 51, 58, 65, 82, 87, 91, 111, 115, 118, 119, 129, 141, 142, 155, 183, 201, 202, 205, 209, 213, 214, 215, 217, 249, 274, 287, 291, 295, 298, 299, 301, 305, 319, 323, 335, 358, 377, 382, 391, 394, 403, 407, 411, 413, 447, 454, 469, 478, 481

Offset: 1

Author

Vladimir Shevelev, Jul 11 2015

Keywords

• nonn

Comments

Conjecturally, the sequence is infinite.

Examples

			65 = 5*13; 65 + 4 = 69 = 3*23. So 65 is in the sequence.
		

Links

• Peter J. C. Moses, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000005, A001358, A005117, A175648.

Programs

Mathematica

Select[Range@ 500, And[SquareFreeQ@ #, PrimeOmega@ # == 2, SquareFreeQ[# + 4], PrimeOmega[# + 4] == 2] &] (* Michael De Vlieger, Jul 12 2015 *)

PARI

main(size)={ v=vector(size); i=0; m=1; while(iAnders Hellström, Jul 11 2015 */

Formula

A000005(a(n)) = A000005(a(n)+4) = 4.

Extensions

More terms from Peter J. C. Moses, Jul 11 2015