A347876 -id:A347876 - cp's OEIS frontend

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A347875 Numbers k such that A323905(sigma(k)) is equal to A323905(2*k).

Original entry on oeis.org

1, 6, 21, 28, 496, 8128

Offset: 1

Antti Karttunen, Sep 19 2021

Numbers k such that A323905(sigma(k)) = A332221(k) - A331750(k) is equal to 2*A156552(k) - A048675(k) = A156552(k) + A323905(k).

Index entries for sequences where odd perfect numbers must occur, if they exist at all

Cf. A000203, A048675, A156552, A323905, A347876.

Cf. also A000396 (subsequence), A331751, A347392.

A048675(n) = { my(f = factor(n)); sum(k=1, #f~, f[k, 2]*2^primepi(f[k, 1]))/2; }; \\ From A048675
A156552(n) = {my(f = factor(n), p, p2 = 1, res = 0); for(i = 1, #f~, p = 1 << (primepi(f[i, 1]) - 1); res += (p * p2 * (2^(f[i, 2]) - 1)); p2 <<= f[i, 2]); res}; \\ From A156552
A323905(n) = (A156552(n) - A048675(n));
isA347875(n) = (A323905(sigma(n))==A323905(2*n));

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