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A264043 Numbers n such that n and n+3 are consecutive semiprimes. 5
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified July 20 22:54 EDT 2019. Contains 325189 sequences. (Running on oeis4.)