A087349 a(n) = n + (smallest prime-factor of n+1).

3, 5, 5, 9, 7, 13, 9, 11, 11, 21, 13, 25, 15, 17, 17, 33, 19, 37, 21, 23, 23, 45, 25, 29, 27, 29, 29, 57, 31, 61, 33, 35, 35, 39, 37, 73, 39, 41, 41, 81, 43, 85, 45, 47, 47, 93, 49, 55, 51, 53, 53, 105, 55, 59, 57, 59, 59, 117, 61, 121, 63, 65, 65, 69, 67, 133, 69, 71, 71

Offset

1,1

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Formula

a(n) = n + A020639(n+1).

a(n) = A061228(n+1) - 1.

Mathematica

a[n_] := n + FactorInteger[n+1][[1, 1]]; Array[a, 100] (* Amiram Eldar, Apr 10 2025 *)

Prog

(Haskell)
a087349 n = a020639 (n + 1) + n  -- Reinhard Zumkeller, Mar 31 2014
(PARI) a(n) = n + factor(n+1)[1, 1]; \\ Amiram Eldar, Apr 10 2025

Crossrefs

Cf. A020639, A061228.

Sequence in context: A348374 A386220 A029639 * A212631 A090792 A076877

Adjacent sequences: A087346 A087347 A087348 * A087350 A087351 A087352

Keyword

nonn,easy

Author

Reinhard Zumkeller, Oct 20 2003

Status

approved