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

1,1

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

Links

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

Example

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.

Prog

(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

Crossrefs

Cf. A001223, A255609, A289750.

Sequence in context: A285600 A191050 A081515 * A184856 A023234 A237662

Adjacent sequences: A289747 A289748 A289749 * A289751 A289752 A289753

Keyword

nonn,easy

Author

Zak Seidov, Jul 11 2017

Status

approved