A321885 a(1) = 1, a(n) = n + d(a(n-1)).

1, 3, 5, 6, 9, 9, 10, 12, 15, 14, 15, 16, 18, 20, 21, 20, 23, 20, 25, 23, 23, 24, 31, 26, 29, 28, 33, 32, 35, 34, 35, 36, 42, 42, 43, 38, 41, 40, 47, 42, 49, 45, 49, 47, 47, 48, 57, 52, 55, 54, 59, 54, 61, 56, 63, 62, 61, 60, 71, 62, 65, 66, 71, 66, 73, 68, 73

Offset

1,2

Comments

Essentially the same as A134488: a(n) = A134488(n) for n >= 5. - Michel Marcus, Nov 21 2018

Links

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

Example

a(6) = 6 + d(a(5)) = 6 + d(9) = 6 + 3 = 9.

Mathematica

a[1]=1; a[n_]:=a[n]=n+DivisorSigma[0, a[n-1]]; Array[a, 50] (* Amiram Eldar, Nov 21 2018 *)
nxt[{n_, a_}]:={n+1, n+1+DivisorSigma[0, a]}; NestList[nxt, {1, 1}, 70][[;; , 2]] (* Harvey P. Dale, Dec 13 2025 *)

Prog

(PARI) seq(n)={my(v=vector(n)); v[1]=1; for(n=2, #v, v[n]=n + numdiv(v[n-1])); v} \\ Andrew Howroyd, Nov 20 2018

Crossrefs

Cf. A000005, A134488.

Sequence in context: A245739 A199187 A098587 * A161182 A267312 A362579

Adjacent sequences: A321882 A321883 A321884 * A321886 A321887 A321888

Keyword

nonn,easy

Author

Todor Szimeonov, Nov 20 2018

Status

approved