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A309502
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Totients congruent to 2 mod 4.
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1
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2, 6, 10, 18, 22, 30, 42, 46, 54, 58, 66, 70, 78, 82, 102, 106, 110, 126, 130, 138, 150, 162, 166, 178, 190, 198, 210, 222, 226, 238, 250, 262, 270, 282, 294, 306, 310, 330, 342, 346, 358, 366, 378, 382, 418, 430, 438, 442, 462, 466, 478, 486, 490, 498, 502
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OFFSET
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1,1
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COMMENTS
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Let the multiplicity of a(n) be the number of m such that phi(m)=a(n), a(1)=2 has multiplicity 3 (phi(3)=phi(4)=phi(6)=2) and all other terms have multiplicity 2 or 4.
Numbers of the form (p-1)*p^e for primes p == 3 (mod 4), e >= 0.
The terms with multiplicity 4 are the numbers in A114874 that are congruent to 2 modulo 4 and greater than 2, that is, the numbers of the form k = (p-1)*p^e for primes p == 3 (mod 4), e >= 1, where k+1 is prime. In this case, the numbers m such that phi(m) = k are m = k+1, 2*(k+1), p^(e+1) and 2*p^(e+1). (End)
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LINKS
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EXAMPLE
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10 = phi(11) = phi(22) and 10 == 2 (mod 4), so 10 is in the sequence.
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PROG
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(PARI) isok(t) = istotient(t) && ((t % 4) == 2); \\ Michel Marcus, Aug 05 2019
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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