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A307108
Numbers x that are equal to lpf(x)*gpf(x)*(lpf(x)+gpf(x))/2, where lpf(x) < gpf(x) are the least and the greatest prime factors of x: A020639 and A006530.
1
105, 231, 627, 897, 935, 1581, 1729, 2465, 2967, 3525, 4123, 4301, 4715, 5487, 7035, 7685, 7881, 9717, 10707, 11339, 14993, 16377, 17353, 17655, 20213, 20915, 23779, 24765, 25327, 26331, 26765, 29341, 29607, 32021, 33335, 34881, 40587, 40807, 42585, 42911, 48635
OFFSET
1,1
EXAMPLE
105 = 3*7*5 is a term, 5 = (3+7) / 2.
231 = 3*11*7 is a term, 7 = (3+11) / 2.
3525 = 3*47*25 is a term, 25 = (3+47) / 2.
PROG
(PARI) is(n) = my(f = factor(n)); omega(f) > 2 && (f[1, 1] * f[#f~, 1]) * (f[1, 1]+f[#f~, 1]) == n << 1 \\ David A. Corneth, Mar 25 2019
CROSSREFS
Cf. A262723 (a squarefree subsequence).
Sequence in context: A375168 A308643 A229094 * A262723 A250757 A350199
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Mar 25 2019
STATUS
approved