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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
OFFSET
1,1
COMMENTS
Conjecturally, the sequence is infinite.
LINKS
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<size, if(omega(m)==2&&omega(m+4)==2&&issquarefree(m)&&issquarefree(m+4), v[i++]=m); m++; ); return(v); } /* Anders Hellström, Jul 11 2015 */
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Jul 11 2015
EXTENSIONS
More terms from Peter J. C. Moses, Jul 11 2015
STATUS
approved