This site is supported by donations to The OEIS Foundation.

Annual Appeal: Today, Nov 11 2014, is the 4th anniversary of the launch of the new OEIS web site. 70,000 sequences have been added in these four years, all edited by volunteers. Please make a donation (tax deductible in the US) to help keep the OEIS running.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A078768 sigma(sigma(..(sigma(n)+1)..)) is prime, or 0 if no prime is reached. 0
 1, 0, 1, 0, 1, 1, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 1, 3, 6, 1, 5, 1, 0, 1, 0, 1, 1, 6, 1, 1, 5, 0, 4, 2, 4, 6, 7, 1, 6, 21, 1, 2, 2, 1, 1, 4, 2, 3, 3, 1, 2, 2, 7, 1, 7, 5, 2, 1, 5, 3, 1, 2, 0, 2, 2, 2, 1, 1, 2, 1, 4, 3, 3, 2, 2, 1, 5, 5, 34, 1, 2, 4, 1, 3, 7, 1, 2, 4, 1, 5, 3, 2, 7, 4, 2, 10, 1, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,18 LINKS EXAMPLE a(18)=3 as sigma(18)+1=40, sigma(40)+1=91, sigma(91)+1=113, which is prime PROG (PARI) sr(m, c)=if (c>0, m=sigma(m)+1; c--; sr(m, c), m) for (n=1, 100, x=1; while (!isprime(sr(n, x)) && x<200, x++); if (x==200, x=0); print1(x", ")) CROSSREFS Sequence in context: A181099 A163327 A175032 * A089078 A134804 A145389 Adjacent sequences:  A078765 A078766 A078767 * A078769 A078770 A078771 KEYWORD nonn AUTHOR Jon Perry, Jan 09 2003 STATUS approved

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

Content is available under The OEIS End-User License Agreement .