A068355 Odd numbers k such that sigma(k)*tau(k) > prime(2*k), where sigma(k) is the sum of divisors of k and tau(k) is the number of divisors of k.

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

Amiram Eldar, Table of n, a(n) for n = 1..10000

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, A000203, A031215.

Sequence in context: A063069 A067828 A144552 * A392495 A331190 A332593

Adjacent sequences: A068352 A068353 A068354 * A068356 A068357 A068358

Keyword

easy,nonn

Author

Benoit Cloitre, Feb 28 2002

Status

approved