A114075 Numbers k such that sigma(k) times k is a cube.

1, 1782, 334800, 2444904, 7555120020, 134099750400, 850719298000

Offset

1,2

Comments

a(8) > 10^12. 200658615201408, 3363643228414950, 6948811926784000, 19056112275200000, 30426038892288000, 63849739291816140, 178779270017085192 and 183497385478330368 are also terms. - Donovan Johnson, May 13 2013

Links

Table of n, a(n) for n=1..7.

Example

sigma(2444904) * 2444904 = 21300003648000 = 27720^3.

Prog

(PARI) is(n)=ispower(n*sigma(n), 3) \\ Charles R Greathouse IV, May 09 2013
(PARI) k=963761198400; rt=sigma(k)/k; for(m=1, 179046067, c=m^3; sr=sqrtint(c); fordiv(c, d, d2=c\d; if(d2/d>rt, next); if(d>sr, next(2)); if(sigma(d)==d2, print(d)))) \\ Donovan Johnson, May 13 2013

Crossrefs

Sequence in context: A255157 A175693 A317628 * A232315 A013593 A152943

Adjacent sequences: A114072 A114073 A114074 * A114076 A114077 A114078

Keyword

nonn,more

Author

Giovanni Resta, Feb 13 2006

Extensions

a(5)-a(6) from Donovan Johnson, May 11 2013

a(7) from Giovanni Resta and Donovan Johnson, May 13 2013

Status

approved