A289750 a(1) = 3 and a(n+1) - a(n) = 2*p where p is the least possible prime.

3, 7, 11, 17, 23, 29, 43, 47, 53, 59, 73, 79, 83, 89, 103, 107, 113, 127, 131, 137, 151, 157, 163, 167, 173, 179, 193, 197, 211, 233, 239, 277, 281, 307, 311, 317, 331, 337, 347, 353, 359, 373, 379, 383, 389, 463, 467, 541, 547, 557, 563, 569, 607, 613, 617, 631, 641, 647, 653, 659

Offset: 1

Author

Zak Seidov, Jul 11 2017

Keywords

• nonn
• easy

Comments

Values of p: 2, 2, 3, 3, 3, 7, 2, 3, 3, 7, 3, 2, 3, 7, 2, 3, 7, 2, 3, 7, 3, 3, 2, 3, 3, 7, 2, 7, 11, 3, 19, 2, 13, 2, 3, 7, 3, 5, 3, 3, 7, 3, 2, 3, 37, 2, 37, 3, 5.

For n > 2, a(n) = A255609(n-1). - Jon E. Schoenfield, Nov 26 2017

Examples

			a(1000) = 23833 = A000040(2651), a(999) = 23819 = A000040(2649), and a(1000)-a(999) = 14 = 2*A000040(4), while 23819 + {4,6,10} are composite.
		

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001223, A255609, A289750.

Programs

PARI

step(n)=forprime(p=2,, if(isprime(n+2*p), return(n+2*p)))
first(n)=my(v=vector(n)); v[1]=3; for(n=2,n, v[n]=step(v[n-1])); v \\ Charles R Greathouse IV, Jul 14 2017