A264043 Numbers n such that n and n+3 are consecutive semiprimes.

6, 22, 35, 46, 62, 74, 82, 115, 155, 166, 206, 259, 262, 295, 323, 355, 358, 362, 395, 466, 478, 482, 502, 511, 559, 562, 583, 586, 611, 623, 626, 671, 703, 718, 731, 734, 746, 755, 763, 799, 835, 838, 862, 866, 886, 895, 914, 923, 955, 979, 982

Offset

1,1

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Formula

a(n) >> n log n. - Charles R Greathouse IV, Nov 02 2015

Example

6 and 9 are 2nd and 3rd semiprimes, or 6=A001358(2) and 9=A001358(3);
22=A001358(8) and 25=A001358(9).

Mathematica

Flatten[Position[Partition[Table[If[PrimeOmega[n]==2, 1, 0], {n, 1000}], 4, 1], _?(#=={1, 0, 0, 1}&)]] (* Harvey P. Dale, Feb 08 2016 *)

Prog

(PARI) for(n=1, 1e3, if(bigomega(n) == 2 && bigomega(n+3) == 2 && bigomega(n+1) !=2 && bigomega(n+2) !=2, print1(n", "))) \\ Altug Alkan, Nov 02 2015
(PARI) is(n)=if(n%4==2, isprime(n/2) && bigomega(n+3)==2 && bigomega(n+1)!=2, n%4==3 && isprime((n+3)/2) && bigomega(n)==2 && bigomega(n+2)!=2) \\ Charles R Greathouse IV, Nov 02 2015

Crossrefs

Cf. A001358, A065516, A136196.

Sequence in context: A046392 A046408 A123017 * A056821 A031083 A218015

Adjacent sequences: A264040 A264041 A264042 * A264044 A264045 A264046

Keyword

nonn

Author

Zak Seidov, Nov 02 2015

Status

approved