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A260021
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Solutions to phi(n) = phi(sigma(n)) that are not given by Theorem 3 of Golomb's manuscript.
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4
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1, 3, 15, 45, 175, 357, 585, 608, 646, 962, 1071, 1292, 1443, 1508, 1586, 1664, 1665, 1898, 2275, 2295, 2379, 2745, 2847, 3285, 3848, 4082, 4329, 4514, 4641, 4736, 4845, 5018, 5402, 6123, 6232, 6344, 6475, 6771, 7052, 7065, 7137, 7202, 7215, 7527, 7592, 7803, 7808, 8103, 8138, 8398, 8541, 8685, 8906, 9344, 9526, 10322
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history;
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OFFSET
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1,2
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REFERENCES
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S. W. Golomb, Equality among number-theoretic functions, Manuscript, no date; Second update, Dec 29, 1992.
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LINKS
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Antti Karttunen, Table of n, a(n) for n = 1..20000
S. W. Golomb, Equality among number-theoretic functions, Unpublished manuscript. (Annotated scanned copy)
Antti Karttunen, Data supplement: n, a(n) computed for n = 1..103800
Index entries for sequences related to sigma(n)
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FORMULA
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{k | 1==A353637(k) and 0==A354344(k)}. - Antti Karttunen, May 25 2022
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PROG
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(PARI)
A354344(n) = { if(!(n%15), n/=15, if(!(n%9), n/=9, if(!(n%8), n/=8, if(!(n%3), n/=3, if(!(n%2), n/=2, return(0)))))); ((n>5) && isprime(n) && isprime((1+n)/2)); };
A353637(n) = (eulerphi(sigma(n))==eulerphi(n));
isA260021(n) = (A353637(n) && !A354344(n)); \\ Antti Karttunen, May 24 2022
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CROSSREFS
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Setwise difference A006872 \ A354345. Subset of positions of zeros in A353636.
Cf. A354362 (subsequence).
Cf. also A005383, A353637, A354344.
Sequence in context: A301632 A074355 A201868 * A005560 A100747 A100737
Adjacent sequences: A260018 A260019 A260020 * A260022 A260023 A260024
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane, Jul 14 2015
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EXTENSIONS
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Term a(1) = 1 prepended and terms a(14) .. a(56) added by Antti Karttunen, May 24 2022
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STATUS
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approved
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