A162886 - OEIS

A162886

Even numbers in an alternating 1-based sum up to some odd nonprime.

24, 42, 54, 60, 78, 84, 96, 114, 132, 138, 144, 150, 168, 174, 180, 186, 204, 216, 222, 234, 240, 258, 264, 276, 282, 294, 306, 312, 324, 330, 348, 354, 366, 372, 384, 390, 402, 414, 420, 432, 438, 444, 450, 456, 474, 480, 486, 492, 504, 510, 516, 528, 534, 546, 558, 564

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Define an alternating sum S(n) = Sum_{k=0..n} (1-(-1)^k*k) = A064455(n+1).

The sequence contains this sum evaluated for an upper limit of the odd nonprimes where the sum is even.

LINKS

Table of n, a(n) for n=1..56.

EXAMPLE

S(n) evaluated at n=1, 9, 15, 21, ... (taken from A014076) is 3, 15, 24, 33, 42, 51, etc., where only the even values (i.e., 24, 42, etc.) join the sequence.

MAPLE

A014076 := proc(n) option remember ; if n = 1 then 1; else for a from procname(n-1)+2 by 2 do if not isprime(a) then RETURN(a) ; fi; od: fi; end:

S := proc(n) A064455(A014076(n)+1) ; end:

for n from 1 to 200 do if S(n) mod 2 = 0 then printf("%d, ", S(n)) ; fi; od: # R. J. Mathar, Jul 21 2009

CROSSREFS

Cf. A014076.

Sequence in context: A062910 A098900 A098769 * A274350 A063702 A074975

Adjacent sequences: A162883 A162884 A162885 * A162887 A162888 A162889

KEYWORD

nonn,less

AUTHOR

Juri-Stepan Gerasimov, Jul 16 2009

EXTENSIONS

Edited and values checked by R. J. Mathar Jul 21 2009

STATUS

approved