The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A177736 Partial sums of A006156. 0
 1, 4, 10, 22, 40, 70, 112, 172, 250, 358, 502, 706, 970, 1312, 1768, 2386, 3184, 4228, 5620, 7450, 9838, 13018, 17164, 22582, 29614, 38812, 50704, 66190, 86410, 112834, 147256, 192118, 250564, 326686, 425962, 555478, 724024, 943540, 1229290 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Partial sums of number of ternary squarefree words of length n. Is this always even after a(0) = 1? If so, there are no prime elements, and the subsequence of semiprime elements begins: 358, 502, 706, 2386, 9838, 112834, 192118, 425962. As Weisstein writes in the Mathworld link from A006156: A "square" word consists of two identical adjacent subwords (for example, acbacb). A squarefree word contains no square words as subwords (for example, abcacbabcb). The only squarefree binary words are a, b, ab, ba, aba, and bab (since aa, bb, aaa, aab, abb, baa, bba, and bbb contain square identical adjacent subwords a, b, a, a, b, a, b, and b, respectively). However, there are arbitrarily long ternary squarefree words. LINKS FORMULA a(n) = Sum_{i=0..n} A006156(i). CROSSREFS Cf. A006156, A060688. Sequence in context: A339609 A008248 A301243 * A061777 A298030 A155369 Adjacent sequences:  A177733 A177734 A177735 * A177737 A177738 A177739 KEYWORD nonn AUTHOR Jonathan Vos Post, May 12 2010 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 24 02:52 EDT 2021. Contains 347620 sequences. (Running on oeis4.)