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A119456 Numbers n such that the Bernoulli number B_{10n} has denominator 66. 29
1, 5, 17, 37, 47, 59, 61, 67, 71, 73, 79, 85, 101, 107, 127, 137, 139, 149, 163, 167, 185, 197, 199, 223, 227, 229, 257, 263, 269, 277, 283, 289, 295, 305, 307, 311, 313, 317, 331, 335, 347, 353, 355, 365, 373, 379, 383, 389, 395, 397, 401, 433, 449, 457, 461 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) is a subset of A002181(n) - Inverse of Euler totient function. Most a(n) are primes except for n=12,21,32,33,34,40,... a(12) = 85 = 5*17, a(21) = 185 = 5*37, a(32) = 289 = 17*17, a(33) = 295 = 5*59, a(34) = 305 = 5*61, a(40) = 335 = 5*67,... Each composite a(n) appears to be a product of two primes from previous a(n) or a square of a prime from previous a(n).

Composite a(n) are the products of powers of previous primes from the a(n). For example, there are a(n) equal to 17, 17^2, 5*17^2, 59^2, 59*61, 61^2, 61*67, 67^2, 67*73, 17^3, 5*17*59, 71*73, 5*17*61, 73^2, 71*79, 73*79, 5*17*73, 79^2, 61*167, 101^2, 37*277, 5*37*59, 79*139, 107^2, 5*17*139, 5*37*67, 5*37*71, 17^2*47, 61*223, 61*227, 5*17*163, 5*17*167, 71*227, 127^2, 17^2*59, 5*59^2, 17^2*61, 5*61^2, 137^2, 137*139, 139^2, 17^2*67, 5*17*229, 137*149, 5*61*67, 5*59*71, 17^2*73, 5*67^2, 5*61*79, 5*67*73, 5*17^3... - Alexander Adamchuk, Jul 28 2006

LINKS

E. PĂ©rez Herrero, Table of n, a(n) for n=1..50000

FORMULA

a(n) = A051230[n]/10. a(n) = A051229[n]/5.

MATHEMATICA

Do[s=1+Divisors[n]; s1=Flatten[Position[PrimeQ[s], True]]; s2=Part[s, s1]; If[Equal[s2, {2, 3, 11}], Print[n/10]], {n, 1, 50000}] - Alexander Adamchuk, Jul 28 2006

CROSSREFS

Cf. A051230, A051229, A002445, A002181.

Sequence in context: A321658 A080167 A060245 * A264904 A257582 A273538

Adjacent sequences:  A119453 A119454 A119455 * A119457 A119458 A119459

KEYWORD

nonn

AUTHOR

Alexander Adamchuk, Jul 26 2006

EXTENSIONS

More terms from Alexander Adamchuk, Jul 28 2006

STATUS

approved

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Last modified April 8 13:35 EDT 2020. Contains 333314 sequences. (Running on oeis4.)