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A280935 Numbers k such that k = rad(k) * sopfr(k), where rad(k) is the squarefree kernel of k and sopfr(k) the integer log of k. 1
16, 27, 72, 540, 2106, 2625, 3264, 5445, 5824, 5880, 10647, 13475, 15210, 15500, 18048, 22800, 28611, 37752, 38528, 39445, 42237, 47334, 61568, 64141, 68952, 69575, 70308, 71136, 71478, 72912, 74115, 75392, 79000, 80937, 83712, 89775, 100156, 100359, 113680, 114660 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Paolo P. Lava, Table of n, a(n) for n = 1..500

EXAMPLE

Prime factors of 2106 are 2, 3, 3, 3, 3, 13. Then rad(2106) = 2 * 3 * 13 = 78, sopfr(2106) = 2 + 3 + 3 + 3 + 3 + 13 = 27 and 78 * 27 = 2106.

MAPLE

with(numtheory): P:=proc(q) local a, k, n; for n from 1 to q do a:=ifactors(n)[2];

if n=mul(a[k][1], k=1..nops(a))*add(a[k][1]*a[k][2], k=1..nops(a)) then print(n);

fi; od; end: P(10^9);

CROSSREFS

Cf. A001414, A007947, A068999.

Sequence in context: A032610 A286429 A329206 * A067650 A123963 A073396

Adjacent sequences:  A280932 A280933 A280934 * A280936 A280937 A280938

KEYWORD

nonn,easy

AUTHOR

Paolo P. Lava, Jan 11 2017

STATUS

approved

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Last modified July 29 22:13 EDT 2021. Contains 346346 sequences. (Running on oeis4.)