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

Offset: 1

Author

Juri-Stepan Gerasimov, Jul 16 2009

Keywords

• nonn
• less

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.

Examples

			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.
		

Crossrefs

Cf. A014076.

Programs

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

Extensions

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