A282844 n-th even semiprime plus n-th odd semiprime.

13, 21, 31, 39, 55, 61, 73, 87, 97, 113, 119, 139, 151, 163, 179, 193, 209, 215, 229, 253, 261, 277, 287, 301, 323, 335, 347, 357, 363, 381, 413, 423, 443, 455, 481, 487, 501, 527, 537, 551, 567, 575, 597, 603

Offset

1,1

Comments

Prime subsequence begins: 13,31,61,73,97,113,139,151,163,179,193.

Semiprime subsequence begins: 21,39,55,87,119,209,215,253,287,301,323.

Links

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

Formula

a(n) = A100484 (n) + A046315 (n).

a(n) ~ 2n log n. - Charles R Greathouse IV, Feb 23 2017

Mathematica

Module[{od=Select[Range[1, 401, 2], PrimeOmega[#]==2&], ev=Select[ Range[ 2, 402, 2], PrimeOmega[#] ==2&], len}, len=Min[Length[od], Length[ev]]; Total/@ Thread[{Take[od, len], Take[ev, len]}]] (* Harvey P. Dale, Jun 07 2018 *)

Prog

(PARI) list(lim)=my(P=2*primes([2, lim\2]), v=List()); forprime(p=3, lim\3, forprime(q=3, min(lim\p, p), listput(v, p*q))); v=Set(v); for(i=1, min(#P, #v), P[i]+=v[i]); P=P[1..min(#P, #v)]; select(k->k<=lim, P) \\ Charles R Greathouse IV, Feb 23 2017

Crossrefs

Cf. A001358, A046315, A100484, A131634.

Sequence in context: A165955 A331116 A050711 * A020440 A164458 A164452

Adjacent sequences: A282841 A282842 A282843 * A282845 A282846 A282847

Keyword

nonn

Author

Zak Seidov, Feb 22 2017

Status

approved