A143407 - OEIS

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A143407

Largest number k such that the reduced totient function psi(k) = A002174(n).

2, 24, 240, 504, 480, 264, 65520, 16320, 28728, 13200, 552, 131040, 6960, 171864, 32640, 138181680, 1082400, 151704, 5520, 1128, 4455360, 12720, 86184, 13920, 1416, 6814407600, 65280, 776664, 18744, 20174525280, 39816, 36801600, 1992

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OFFSET

1,1

COMMENTS

For each of the values in A002174, there are only a finite number of numbers k such that psi(k)=A002174(n). This sequence gives the largest such k. Sequence A002396 gives the least k. The number of such k is given in A143408. When A002174(n) is twice a Sophie Germain prime, then a(n) is particularly small.

LINKS

T. D. Noe, Table of n, a(n) for n=1..1000

FORMULA

a(n) = A006863(A002174(n)/2) for n>1.

CROSSREFS

Cf. A002322 (reduced totient function), A002174, A002396, A143408.

Sequence in context: A219205 A025131 A270564 * A366155 A228619 A252764

Adjacent sequences: A143404 A143405 A143406 * A143408 A143409 A143410

KEYWORD

nonn

AUTHOR

T. D. Noe, Aug 13 2008

STATUS

approved