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.

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

Links

Table of n, a(n) for n=1..41.

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. A020639, A006530.

Cf. A262723 (a squarefree subsequence).

Sequence in context: A375168 A308643 A229094 * A262723 A250757 A350199

Adjacent sequences: A307105 A307106 A307107 * A307109 A307110 A307111

Keyword

nonn

Author

_Alex Ratushnyak_, Mar 25 2019

Status

approved