A066820 Integers of the form phi(n^2+1)/n.

1, 2, 4, 6, 6, 10, 14, 16, 20, 24, 26, 25, 36, 40, 48, 54, 56, 60, 66, 74, 84, 90, 94, 110, 116, 120, 124, 126, 98, 130, 134, 146, 150, 156, 160, 170, 176, 180, 184, 150, 204, 206, 210, 192, 224, 230, 236, 240, 250, 256, 260, 264, 270, 280, 284, 300, 306, 314, 326

Offset

1,2

Comments

If k^2 + 1 is prime, phi(k^2 + 1)/k = k, hence A005574(n) is included in the sequence. For odd values see A066852.

Links

Harry J. Smith, Table of n, a(n) for n = 1..1000

Prog

(PARI) { n=0; for (m=1, 10^10, if (eulerphi(m^2 + 1) % m == 0, write("b066820.txt", n++, " ", eulerphi(m^2 + 1) / m); if (n==1000, return)) ) } \\ Harry J. Smith, Mar 29 2010

Crossrefs

Cf. A066852.

Sequence in context: A254733 A254732 A299541 * A309796 A359671 A222733

Adjacent sequences: A066817 A066818 A066819 * A066821 A066822 A066823

Keyword

nonn

Author

Benoit Cloitre, Jan 19 2002

Extensions

Term n=51 a=260 added by Harry J. Smith, Mar 29 2010

Status

approved