login
This site is supported by donations to The OEIS Foundation.
Logo

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A109824 a(n) is the number of consecutive integers starting with n summing up to a semiprime. 2
3, 3, 5, 1, 4, 1, 2, 4, 1, 1, 5, 2, 4, 1, 1, 2, 2, 3, 2, 4, 1, 1, 13, 2, 1, 1, 2, 2, 4, 3, 6, 2, 1, 1, 1, 3, 6, 1, 1, 3, 5, 2, 2, 7, 2, 1, 2, 6, 1, 4, 1, 3, 4, 6, 1, 7, 1, 1, 2, 2, 2, 1, 6, 2, 1, 2, 4, 4, 1, 2, 2, 2, 4, 1, 14, 6, 1, 3, 2, 2, 5, 1, 13, 2, 1, 1, 1, 2, 4, 14, 1, 2, 1, 1, 1, 3, 4, 4, 5, 2 (list; graph; refs; listen; history; internal format)
OFFSET

1,1

FORMULA

A109824(n) = A109823(n) - n + 1.

PROG

(PARI) {issemiprime(n) = local(f); f = factorint(n)[, 2]; sum(i = 1, length(f), f[i]) == 2}{a2(n) = local(s, m); s=n; m=n; while(!issemiprime(s), m++; s+=m); m-n+1}

CROSSREFS

Cf. A109411, A109823.

Sequence in context: A021753 A062563 A091931 * A011399 A205853 A079887

Adjacent sequences:  A109821 A109822 A109823 * A109825 A109826 A109827

KEYWORD

nonn

AUTHOR

Zak Seidov (zakseidov(AT)yahoo.com) & Max Alekseyev (maxale(AT)gmail.com), Jul 03 2005

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

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

Last modified February 17 12:38 EST 2012. Contains 206021 sequences.