A238264 Smallest number that can be written in the form 2^k1 * p1^k2 + 2^k3 * p2^k4 in exactly n distinct ways, where p1 and p2 are odd prime numbers and k1,k2,k3,k4 are nonnegative integers.

2, 4, 6, 8, 10, 12, 14, 18, 20, 24, 26, 28, 30, 36, 42, 45, 48, 50, 56, 54, 60, 80, 72, 81, 93, 84, 115, 90, 110, 105, 114, 108, 129, 120, 132, 144, 153, 205, 150, 165, 186, 168, 189, 195, 204, 180, 231, 216, 234, 246, 210, 279, 276, 255, 240, 252, 288, 270

Offset

1,1

Comments

a(n) is the smallest index k of A238263(k) for all k-s such that A238263(k)=n.

Links

Lei Zhou, Table of n, a(n) for n = 1..10000

Example

A238263(2)=A238263(3)=1, Min[2,3]=2, so a(1)=2.
...
A238263(50)=A238263(51)=...=A238263[71]=18, Min[50, 51,...,71]=50, so a(18)=50.

Mathematica

n = 1; found = 0; s = {}; target = 58; Do[AppendTo[s, 0], {i, 1, target}]; While[found < target, n++; ct = 0; Do[If[f1 = FactorInteger[i]; l1 = Length[f1]; If[f1[[1, 1]] == 2, l1--]; f2 = FactorInteger[n - i]; l2 = Length[f2]; If[f2[[1, 1]] == 2, l2--]; (l1 <= 1) && (l2 <= 1), ct++], {i, 1, Floor[n/2]}]; If[ct <= target, If[s[[ct]] == 0, s[[ct]] = n; found++]]]; s

Crossrefs

Cf. A238263, A000961.

Sequence in context: A076828 A276106 A321501 * A098807 A189562 A194372

Adjacent sequences: A238261 A238262 A238263 * A238265 A238266 A238267

Keyword

nonn

Author

Lei Zhou, Feb 21 2014

Status

approved