A158339 Semiprimes that are the sum of four successive semiprimes.

39, 94, 106, 118, 146, 158, 185, 201, 221, 254, 302, 365, 427, 473, 485, 519, 537, 589, 633, 655, 707, 723, 749, 767, 842, 851, 869, 901, 1003, 1145, 1205, 1211, 1219, 1247, 1263, 1337, 1349, 1603, 1646, 1681, 1703, 1731, 1797, 1891, 1903, 1937, 2005, 2019

Offset: 1

Author

Zak Seidov, Mar 16 2009

Keywords

• nonn

Examples

			a(1)=39=6+9+10+14, or A001358(15)=A001358(2)+A001358(3)+A001358(4)+A001358(5).
		

Links

• Zak Seidov, Table of n, a(n) for n = 1..100000

Crossrefs

Semiprimes that are the sum of k successive semiprimes: A131610 (k=3), A092192 (k=2), A001358 (k=1).

Programs

Mathematica

Select[Total/@Partition[Select[Range[600],PrimeOmega[#]==2&],4,1], PrimeOmega[ #]==2&] (* Harvey P. Dale, Aug 14 2014 *)

PARI

issemi(n)=bigomega(n)==2
list(lim)=if(lim<39, return([])); my(v=List(), u=v, x=lim\4+log(lim)*4\1+9); forprime(p=2,x\2, forprime(q=2,min(x\p,p), listput(u,p*q))); u=Set(u); while(u[#u-2]+u[#u-1]+u[#u]+x+1<=lim, while(!issemi(x++),); u=concat(u,x)); for(i=1,#u-3, u[i]+=u[i+1]+u[i+2]+u[i+3]); u[#u-2]=u[#u-1]=u[#u]=1; forprime(p=2,lim\2, forprime(q=2,min(lim\p,p), listput(v,p*q))); setintersect(Set(v), u) \\ Charles R Greathouse IV, Mar 05 2017