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A128462 Nontrivial products of two lucky numbers. 1
9, 21, 27, 39, 45, 49, 63, 75, 81, 91, 93, 99, 105, 111, 117, 129, 135, 147, 153, 169, 175, 189, 195, 201, 207, 217, 219, 225, 231, 237, 259, 261, 273, 279, 297, 301, 315, 325, 333, 343, 345, 357, 375, 381, 387, 399, 403, 405, 423, 429, 441, 453, 459, 465, 469 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This is to Lucky numbers (A000959) greater than 1, as semiprimes (A001358) are to primes (A000040). Since A000959(1) = 1, dropping the word "nontrivial" gives "product of two lucky numbers" = {a(i)} UNION A000959 = {1, 3, 7, 9, 13, 15, 21, 25, 27, 31, 33, 37, 39, 43, 45, 49, 51, 63, 67, 69, 73, 75, 79, 81, 87, 91, 93, 99, ...}.

LINKS

Table of n, a(n) for n=1..55.

FORMULA

Product set of {A000959(n) for n>1} = {A000959(i)*A000959(j) for i, j > 1}.

CROSSREFS

Cf. A000959, A001358.

Sequence in context: A053795 A100490 A173250 * A186815 A106214 A036316

Adjacent sequences:  A128459 A128460 A128461 * A128463 A128464 A128465

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, May 05 2007

EXTENSIONS

99 =3*33 and 175 inserted, sequence extended - R. J. Mathar, Oct 22 2010

STATUS

approved

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Last modified May 12 10:17 EDT 2021. Contains 343821 sequences. (Running on oeis4.)