A155101 Nonprimes k such that the sum of prime factors of composite(k) is an even composite.

1, 4, 8, 9, 10, 12, 15, 20, 21, 24, 26, 28, 33, 34, 35, 38, 40, 42, 45, 46, 49, 50, 51, 55, 56, 58, 60, 63, 66, 68, 70, 72, 74, 75, 80, 81, 84, 88, 90, 92, 96, 98, 99, 100, 102, 104, 105, 106, 108, 110, 117, 118, 119, 121, 123, 124, 128, 129, 130, 133, 136, 140, 142, 143

Offset

1,2

Links

Table of n, a(n) for n=1..64.

Example

1 (nonprime) is a term because composite(1) = 4 = 2*2 and 2 + 2 = 4 is an even composite;
4 (nonprime) is a term because composite(4) = 9 = 3*3 and 3 + 3 = 6 is an even composite;
8 (nonprime) is a term because composite(8) = 15 = 3*5 and 3 + 5 = 8 is an even composite.

Maple

pss := proc(n) local a, d ; a := 0 ; for d in ifactors(n)[2] do a := a+ op(2, d)*op(1, d) ; end do: a ; end proc:
isA002808 := proc(n) n >= 4 and not isprime(n) ; end proc:
A002808 := proc(n) option remember ; local a; if n = 1 then 4; else for a from procname(n-1)+1 do if not isprime(a) then return a; end if; end do; end if; end proc:
for n from 1 to 400 do if not isprime(n) then c := pss(A002808(n)) ; if type(c, 'even') and isA002808(c) then printf("%d, ", n) ; end if; end if; end do: # R. J. Mathar, May 10 2010

Crossrefs

Cf. A000027, A002808, A141468.

Sequence in context: A096529 A351099 A193166 * A158582 A144754 A080970

Adjacent sequences: A155098 A155099 A155100 * A155102 A155103 A155104

Keyword

nonn

Author

Juri-Stepan Gerasimov, Jan 20 2009

Extensions

Corrected (44 removed, 80 inserted) by R. J. Mathar, May 10 2010

Status

approved