A155878 a(0)=4; for n > 0, a(n) is the smallest composite number c > a(n-1) such that c + n is also composite.

4, 8, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 26, 27, 28, 30, 32, 33, 34, 35, 36, 39, 40, 42, 44, 45, 46, 48, 49, 51, 52, 54, 55, 57, 58, 60, 62, 63, 64, 65, 66, 69, 70, 72, 74, 75, 76, 77, 78, 80, 82, 84, 86, 87, 88, 90, 91, 93, 94, 95, 96, 98, 99, 102, 104, 105, 106, 108

Offset

0,1

Links

Table of n, a(n) for n=0..67.

Example

a(0)=4. Adding a(0) to n=0 gives 4+0=4, which is a composite number; adding a(1) to n=1 gives 8+1=9 which is composite; adding a(2) to n=2 gives 10+2=12 which is composite; adding a(3) to n=3 gives 12+3=15 which is composite; etc.

Maple

isA002808 := proc(n) option remember; RETURN(n>= 4 and not isprime(n)) ; end: A155878:= proc(n) option remember; local a; if n = 0 then 4; else for a from procname(n-1)+1 do if isA002808(a) and isA002808(a+n) then RETURN(a) ; fi; od: fi; end: seq(A155878(n), n=0..100) ; # R. J. Mathar, Jan 31 2009

Crossrefs

Cf. A155874.

Sequence in context: A310974 A310975 A310976 * A029886 A102218 A257586

Adjacent sequences: A155875 A155876 A155877 * A155879 A155880 A155881

Keyword

base,easy,nonn

Author

Eric Angelini, Jan 29 2009

Extensions

Extended by R. J. Mathar, Jan 31 2009

Name edited by Jon E. Schoenfield, Jan 20 2019

Status

approved