A036060 Number of 3-component Carmichael numbers C = (6M + 1)(12M + 1)(18M + 1) < 10^n.

0, 1, 1, 2, 2, 3, 7, 10, 16, 25, 50, 86, 150, 256, 436, 783, 1435, 2631, 4765, 8766, 16320, 30601, 57719, 109504, 208822, 400643, 771735, 1494772, 2903761, 5658670, 11059937, 21696205, 42670184, 84144873, 66369603, 329733896, 655014986, 1303918824, 2601139051

Offset: 3

Author

N. J. A. Sloane

Keywords

• nonn

Comments

Note that this is different from the count of 3-Carmichael numbers, A132195. The numbers counted here are neither those listed in A087788 (3 arbitrary prime factors) nor those listed in A033502 (where 6m + 1, 12m + 1 and 18m + 1 are all prime). - M. F. Hasler, Apr 14 2015

References

• Posting by Harvey Dubner (harvey(AT)dubner.com) to Number Theory List (NMBRTHRY(AT)LISTSERV.NODAK.EDU), Nov 23 1998.

Links

• Amiram Eldar, Table of n, a(n) for n = 3..42
• H. Dubner, 3-Component Carmichael Numbers-correction, Post to Number Theory List, Nov 23 1998.
• Harvey Dubner, Carmichael Numbers of the form (6m+1)(12m+1)(18m+1), Journal of Integer Sequences, Vol. 5 (2002), Article 02.2.1.
• Index entries for sequences related to Carmichael numbers.

Crossrefs

Cf. A002997, A033502, A055553, A087788, A132195.

Extensions

Terms updated (from Dubner's paper) by Amiram Eldar, Aug 11 2017