A259312 n such that 3 < sigma(n)/n < sigma(m)/m for all abundant numbers m

180, 780, 1872, 2352, 16830, 17850, 20496, 51060, 59724, 64890, 430272, 884730, 3767100, 4946508, 15287976, 33806052, 34747416, 40974318, 137168580, 140492772, 157048290, 184773312, 3615557148, 16709332608, 40564903620, 40936559976, 60782804964

Offset: 1

Author

Michel Marcus, Jun 24 2015

Keywords

• nonn

Comments

This sequence is similar to A071927, but with ratio 3 rather than 2.

a(28) > 7*10^10. - Giovanni Resta, Jun 24 2015

Crossrefs

Cf. A068403 (sigma(n)>3n), A071927 (barely abundant).

Programs

PARI

lista(nn) =  {abk = 4; for (n = 1, nn, ab = sigma(n)/n; if ((ab > 3) && (ab < abk), print1(n, ", "); abk = ab););}

Extensions

a(23)-a(27) from Giovanni Resta, Jun 24 2015