A068355 Odd n such that sigma(n)*tau(n)>prime(2*n) where sigma(n) is the sum of divisors of n and tau(n) the number of divisors of n = A000005(n).

45, 105, 135, 165, 195, 225, 315, 405, 495, 525, 567, 585, 675, 693, 735, 765, 819, 825, 855, 945, 975, 1035, 1071, 1125, 1155, 1197, 1215, 1275, 1287, 1305, 1323, 1365, 1395, 1425, 1449, 1485, 1575, 1617, 1665, 1683, 1701, 1725, 1755, 1785, 1815

Offset

1,1

Links

Table of n, a(n) for n=1..45.

Mathematica

Select[Range[1, 1901, 2], DivisorSigma[1, #]DivisorSigma[0, #]>Prime[2#]&] (* Harvey P. Dale, Feb 17 2015 *)

Prog

(PARI) for(n=1, 2200, if(sigma(n)*numdiv(n)*(1-(-1)^n)/2>prime(2*n), print1(n, ", ")))

Crossrefs

Cf. A000005.

Sequence in context: A063069 A067828 A144552 * A331190 A332593 A144486

Adjacent sequences: A068352 A068353 A068354 * A068356 A068357 A068358

Keyword

easy,nonn

Author

Benoit Cloitre, Feb 28 2002

Status

approved