A256862 a(1)=1, then a(n) = least number > a(n-1) such that 2*a(n-1)+a(n) is prime.

1, 3, 5, 7, 9, 11, 15, 17, 19, 21, 25, 29, 31, 35, 37, 39, 49, 51, 55, 57, 59, 61, 69, 73, 77, 79, 81, 89, 91, 95, 103, 105, 107, 117, 119, 121, 125, 129, 131, 135, 139, 141, 149, 151, 155, 157, 165, 169, 171, 179, 183, 191, 195, 197, 199, 201, 205, 207, 217, 219, 221, 231, 239

Offset

1,2

Comments

I conjecture that any initial term a(1) eventually merges with this sequence.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

a=1; s={a}; Do[x=a+1+Mod[a, 2]; While[!PrimeQ[2*a+x], x=x+2]; s={s, x}; a=x, {100}]; s=Flatten[s]
lngp[n_]:=Module[{k=n+1}, While[!PrimeQ[2n+k], k++]; k]; NestList[lngp, 1, 70] (* Harvey P. Dale, Jan 04 2025 *)

Prog

(PARI) v=[1]; n=2; while(#v<100, if(isprime(2*v[#v]+n), v=concat(v, n)); n++); v \\ Derek Orr, Apr 14 2015

Crossrefs

Sequence in context: A340718 A155113 A327260 * A173601 A165705 A209492

Adjacent sequences: A256859 A256860 A256861 * A256863 A256864 A256865

Keyword

nonn,easy

Author

Zak Seidov, Apr 11 2015

Status

approved