A131634 - OEIS

A131634

n-th even semiprime minus n-th odd semiprime.

-5, -9, -11, -11, -11, -9, -5, -11, -5, 3, 5, 9, 13, 9, 9, 19, 27, 29, 39, 31, 31, 39, 45, 55, 65, 69, 65, 71, 73, 71, 95, 101, 105, 101, 115, 117, 127, 125, 131, 141, 149, 149, 167, 169, 175, 177, 187, 209, 207, 209, 213, 219, 217, 235, 227, 237, 247, 247, 255, 261, 263, 281, 305, 303, 305, 311, 335, 345, 359, 359, 365, 363

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Starting with n=10, n-th even semiprime > n-th odd semiprime. Sequence is not monotonic, with general increasing trend.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

FORMULA

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

MATHEMATICA

Module[{semis=Select[Range[1000], PrimeOmega[#]==2&], ev, od, len}, ev = Select[ semis, EvenQ]; od=Select[semis, OddQ]; len=Min[Length[ ev], Length[ od]]; First[#]- Last[#]&/@Thread[{Take[ev, len], Take[od, len]}]] (* Harvey P. Dale, Apr 20 2014 *)

CROSSREFS

Cf. A046315, A100484.

Sequence in context: A119124 A326769 A331005 * A049049 A118358 A101731

Adjacent sequences: A131631 A131632 A131633 * A131635 A131636 A131637

KEYWORD

sign,easy

AUTHOR

Zak Seidov, Oct 02 2007

STATUS

approved