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 A332445 Numbers k of the form 4m+1 for which A087808(sigma(k)) is equal to 2*A087808(k). 5
 2009, 19377, 37809, 59373, 74673, 115677, 270041, 310329, 354609, 357309, 720425, 732321, 841437, 2071737, 2612269, 3131149, 3866461, 3930929, 5172093, 5593981, 7118753, 7903961, 8224173, 9327393, 9438129, 11452321, 12708025, 18857209, 18861889, 18875313, 19110321, 20278269, 20709225, 20950061, 23963597, 24895153 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers k such that A332224(k) is equal to A087808(2*k) and k == 1 mod 4. Notably, the only square among the first 299 terms is a(248) = 5808421369 = 76213^2. sigma(5808421369) = 5808497583 == 3 (mod 4) == 7 (mod 8). Of the remaining 298 terms < 2^33, 92 are such that sigma(k) == 6 (mod 8) and 206 are such that sigma(k) == 2 (mod 8), that is, are terms of A332227. Question: Why the terms come in clusters? Compare also the scatterplots of A087808 and A332224, and a similar sequence A332465. LINKS Antti Karttunen, Table of n, a(n) for n = 1..299; all terms <= 2^33 PROG (PARI) A087808(n) = if(n<1, 0, if(n%2==0, 2*A087808(n/2), A087808((n-1)/2)+1)); isA332445(n) = ((1==(n%4))&&(2*A087808(n)==A087808(sigma(n)))); CROSSREFS Intersection of A016813 and A332446. Cf. also A228058, A332227, A332465. Cf. A000203, A087808, A286357, A332224, A332225, A332458. Sequence in context: A172807 A153822 A153779 * A162242 A249955 A020433 Adjacent sequences: A332442 A332443 A332444 * A332446 A332447 A332448 KEYWORD nonn AUTHOR Antti Karttunen, Feb 14 2020 STATUS approved

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Last modified January 28 14:10 EST 2023. Contains 359895 sequences. (Running on oeis4.)