A138786 -id:A138786 - cp's OEIS frontend

A140607 (A039649(2n+1)+A137576(n))/2.

3, 5, 7, 10, 11, 13, 13, 17, 19, 22, 23, 31, 37, 29, 31, 31, 43, 37, 37, 41, 43, 55, 47, 64, 45, 53, 61, 55, 59, 61, 55, 61, 67, 78, 71, 73, 91, 106, 79, 136, 83, 77, 85, 89, 91, 96, 109, 97, 136, 101, 103, 109, 107, 109, 109, 113, 155, 103, 145, 166, 111, 201, 127, 113

Offset: 1

Vladimir Shevelev, May 18 2008

nonn

If 2n+1 is a prime then a(n) = 2n+1.

Ray Chandler, Table of n, a(n) for n=1..10000

Cf. A039649, A137576, A000010, A000040, A140140, A138193, A138217, A138227, A138535, A138536, A138537, A138539, A140141, A140608, A138786, A140667.

Extended by Ray Chandler, May 20 2008, May 24 2008

A140608 "Right" odd composite numbers n for which n > A140607((n-1)/2).

Original entry on oeis.org

15, 33, 39, 51, 57, 63, 65, 85, 87, 111, 117, 123, 129, 145, 159, 171, 177, 183, 185, 195, 201, 205, 249, 255, 265, 273, 275, 291, 303, 305, 315, 321, 327, 333, 339, 341, 393, 399, 411, 417, 435, 447, 451, 455, 465, 471, 481, 485, 489, 505, 511, 513, 519, 537

Offset: 1

Vladimir Shevelev, May 18 2008

nonn

Conjecture. The sequence is infinite.

Ray Chandler, Table of n, a(n) for n=1..2022

Cf. A140607, A039649, A140140, A138193, A138217, A138227, A138535, A138536, A138537, A138539, A140141, A000010, A000040, A138786, A140667.

Extended by Ray Chandler, May 20 2008

A140667 Odd composite numbers k for which k = A140607((k-1)/2).

Original entry on oeis.org

91, 1581, 2465, 8481, 25761, 31609, 33355, 34945, 118405, 146611, 319507, 736291, 994507, 3270403, 3375487, 5176153, 6186403, 6228685, 8650951, 10679131, 22028203, 26017291, 31470211, 33796531, 41710411, 42149971, 42474547, 46672291, 48316969, 49019851, 58986091, 68182003, 69885649

Offset: 1

Ray Chandler, May 20 2008

nonn

Cf. A140607, A039649, A140140, A138193, A138217, A138227, A138535, A138536, A138537, A138539, A140141, A000010, A000040, A140608, A138786.

f(n) = (eulerphi(2*n+1) + 1 + g(n))/2; \\ A140607
g(n) = sumdiv(2*n+1, d, eulerphi(d)/(t=znorder(Mod(2, d))))*t-t+1; \\ A137576
isok(c) = if (!isprime(c) && (c%2), f((c-1)/2) == c); \\ Michel Marcus, Jan 31 2023

More terms from Michel Marcus, Jan 31 2023

cp's OEIS Frontend

A140607 (A039649(2n+1)+A137576(n))/2.

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A140608 "Right" odd composite numbers n for which n > A140607((n-1)/2).

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Extensions

A140667 Odd composite numbers k for which k = A140607((k-1)/2).

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