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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. 3
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified December 8 20:37 EST 2021. Contains 349596 sequences. (Running on oeis4.)