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A308220 Number of irreducible Egyptian fractions of denominator n which are the sum of 2 unit fractions. 3
2, 2, 3, 3, 4, 3, 4, 4, 5, 4, 6, 4, 4, 5, 5, 5, 6, 5, 6, 6, 8, 4, 8, 6, 6, 7, 8, 7, 8, 6, 6, 7, 7, 7, 10, 7, 4, 7, 11, 8, 8, 7, 6, 8, 9, 5, 10, 9, 8, 9, 9, 9, 8, 7, 12, 9, 10, 6, 12, 9, 4, 8, 11, 9, 12, 9, 6, 10, 12, 8, 12, 10, 4, 9, 13, 10, 13, 7, 10, 11, 10, 6, 12, 12, 10, 9, 12, 10, 12, 10, 10, 9, 10, 7, 12, 11, 6, 11, 13, 12 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..100.

Cyril Banderier, Florian Luca, Francesco Pappalardi, Numerators of Egyptian fractions, 2019.

FORMULA

For p prime, a(p) = number_of_divisors(p+1).

EXAMPLE

There are a(2)=2 irreducible fractions with denominator n=2 which are sums of 2 unit fractions: 1/2 = 1/4 + 1/4 and 3/2 = 1/1 + 1/2.

CROSSREFS

Cf. A308219, A308221, A308415.

Sequence in context: A014701 A207034 A226164 * A302039 A056239 A161511

Adjacent sequences:  A308217 A308218 A308219 * A308221 A308222 A308223

KEYWORD

nonn

AUTHOR

Cyril Banderier, May 15 2019

STATUS

approved

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Last modified December 5 10:11 EST 2021. Contains 349543 sequences. (Running on oeis4.)