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A283486 Number of k such that sigma(k) = 2n where sigma(m) = A000203(m) is the sum of the divisors of m. 2
0, 1, 1, 1, 0, 2, 1, 0, 2, 1, 0, 3, 0, 1, 1, 2, 0, 1, 1, 1, 3, 1, 0, 3, 0, 0, 2, 2, 0, 3, 1, 0, 0, 1, 0, 5, 1, 0, 1, 2, 0, 3, 0, 0, 3, 0, 0, 4, 2, 0, 1, 2, 0, 2, 1, 1, 2, 0, 0, 4, 0, 2, 2, 2, 0, 2, 0, 0, 1, 2, 0, 5, 0, 0, 1, 2, 0, 2, 1, 1, 1, 1, 0, 6, 0, 0, 1, 1, 0, 4, 2, 0, 2, 0, 0, 5 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

COMMENTS

First occurrence of k: 1, 2, 6, 12, 48, 36, 84, ...

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A054973(2n) - Michel Marcus, Mar 08 2017.

EXAMPLE

a(12) = 3 because sigma(14) = 1 + 2 + 7 + 14 = 24, sigma(15) = 1 + 3 + 5 + 15 = 24 and sigma(23) = 1 + 23 = 24.

PROG

(PARI) first(n)=my(v=vector(n), t); for(k=1, 2*n-1, t=sigma(k)/2; if(t<=n && denominator(t)==1, v[t]++)); v \\ Charles R Greathouse IV, Mar 08 2017

CROSSREFS

Cf. A000203, A054973, A060658.

Sequence in context: A110658 A002188 A128313 * A330759 A216607 A025672

Adjacent sequences:  A283483 A283484 A283485 * A283487 A283488 A283489

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Mar 08 2017

EXTENSIONS

a(96) corrected by Charles R Greathouse IV, Mar 08 2017

STATUS

approved

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Last modified June 6 17:20 EDT 2020. Contains 334829 sequences. (Running on oeis4.)