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A282844 n-th even semiprime plus n-th odd semiprime. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 20 13:06 EST 2022. Contains 350472 sequences. (Running on oeis4.)