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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A181522 Number of subsets of {1,2,...,n} whose sum is semiprime (cf. A001358, A064911). 3
0, 0, 2, 6, 13, 25, 47, 92, 184, 367, 721, 1416, 2769, 5407, 10662, 21135, 41866, 83220, 166617, 334852, 670725, 1334868, 2650263, 5280475, 10567613, 21145411, 42103939, 83382359, 164843079, 326791838, 650995628, 1301718424, 2605360702, 5205671338, 10369588530 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..400

EXAMPLE

a(4) = #{{1,3}, {4}, {1,2,3}, {2,4}, {2,3,4}, {1,2,3,4}} = 6.

PROG

(Haskell)

import Data.List (subsequences)

a181522 = length . filter ((== 1) . a064911 . sum) .

                          subsequences . enumFromTo 1

-- Reinhard Zumkeller, Feb 22 2012, Oct 27 2010

CROSSREFS

Cf. A127542, A126024.

Cf. A064911.

Sequence in context: A065220 A048094 A335439 * A031872 A259577 A172348

Adjacent sequences:  A181519 A181520 A181521 * A181523 A181524 A181525

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Oct 27 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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 5 04:03 EDT 2021. Contains 346457 sequences. (Running on oeis4.)