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 A255746 Squarefree semiprimes n such that n+4 is also a squarefree semiprime. 2
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Conjecturally, the sequence is infinite. LINKS Peter J. C. Moses, Table of n, a(n) for n = 1..1000 FORMULA A000005(a(n)) = A000005(a(n)+4) = 4. EXAMPLE 65 = 5*13; 65 + 4 = 69 = 3*23. So 65 is in the sequence. MATHEMATICA Select[Range@ 500, And[SquareFreeQ@ #, PrimeOmega@ # == 2, SquareFreeQ[# + 4], PrimeOmega[# + 4] == 2] &] (* Michael De Vlieger, Jul 12 2015 *) PROG (PARI) main(size)={ v=vector(size); i=0; m=1; while(i

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Last modified November 18 21:04 EST 2018. Contains 317331 sequences. (Running on oeis4.)