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A227248 Composite numbers such that sum_{i=1..k} (p_i/(p_i+1))/product_{i=1..k} (p_i/(p_i+1)) is an integer, where p_i are the k prime factors of n (with multiplicity). 5
4, 72, 102, 216, 260, 264, 270, 432, 462, 504, 612, 720, 1980, 2592, 3672, 5184, 5550, 8352, 10368, 15552, 20736, 22032, 25488, 29016, 30240, 31104, 36288, 38880, 41976, 46656, 49248, 57888, 62208, 93312, 103680, 132192, 186624, 238464, 286848, 373248, 410688 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Paolo P. Lava, Table of n, a(n) for n = 1..65

EXAMPLE

Prime factors of 270 are 2, 3^3, 5; therefore (2/(2+1)+3*3/(3+1)+5/(5+1))/(2/(2+1)*(3/(3+1))^3*5/(5+1)) = 16.

MAPLE

with(numtheory); ListA227248:=proc(q) local a, d, n, p;

for n from 2 to q do if not isprime(n) then p:=ifactors(n)[2];

a:=add((op(1, d)/(op(1, d)+1))*op(2, d), d=p)/mul((op(1, d)/(op(1, d)+1))^op(2, d), d=p);

if type(a, integer) then print(n); fi; fi;

od; end: ListA227248(10^10);

CROSSREFS

Cf. A224346, A224912, A226365, A227034.

Sequence in context: A161791 A132097 A128062 * A113839 A077112 A203537

Adjacent sequences:  A227245 A227246 A227247 * A227249 A227250 A227251

KEYWORD

nonn

AUTHOR

Paolo P. Lava, Jul 04 2013

STATUS

approved

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Last modified June 27 08:21 EDT 2017. Contains 288777 sequences.