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

1,1

Links

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

Example

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

Mathematica

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

Prog

(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

Crossrefs

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

Sequence in context: A043245 A044025 A062668 * A211499 A126077 A276401

Adjacent sequences: A158336 A158337 A158338 * A158340 A158341 A158342

Keyword

nonn

Author

Zak Seidov, Mar 16 2009

Status

approved