A107819 Slowest increasing sequence where a(n)+n is prime.

1, 3, 4, 7, 8, 11, 12, 15, 20, 21, 26, 29, 30, 33, 38, 43, 44, 49, 52, 53, 58, 61, 66, 73, 76, 77, 80, 81, 84, 97, 100, 105, 106, 115, 116, 121, 126, 129, 134, 139, 140, 149, 150, 153, 154, 165, 176, 179, 180, 183

Offset: 1

Author

Eric Angelini, Jun 11 2005

Keywords

• easy
• nonn

Comments

Appears to be closely related to A014692.

Examples

			(1)+1=2, which is prime; (3)+2=5=prime; (4)+3=7=prime; (7)+4=11=prime; (8)+5=13=prime; etc.
		

Programs

Maple

A107819 := proc(n)
        option remember;
        if n = 1 then
                return 1;
        else
                for a from procname(n-1)+1 do
                        if isprime(a+n) then
                                return a;
                        end if;
                end do:
        end if;
end proc: # R. J. Mathar, Sep 05 2011

Sage

@cached_function
def A107819(n):
    prev = (-1 if n == 1 else A107819(n-1))
    return next_prime(prev+n)-n  # D. S. McNeil, Sep 05 2011

Extensions

Corrected by R. J. Mathar, Sep 05 2011