A133688 - OEIS

A133688

Least odd primitive abundant number with 3^n as a divisor, but not 3^(n+1).

5391411025, 5775, 1575, 945, 81081, 78975, 1468935, 6375105, 436444281, 5356826865, 21873816315, 371922783705, 2241870572475, 158639164165575

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OFFSET

0,1

LINKS

Table of n, a(n) for n=0..13.

EXAMPLE

5391411025=3^0*5^2*7*11*13*17*19*23*29 least odd abundant number with no factor 3

5775=3^1*5^2*7*11

1575=3^2*5^2*13

945=3^3*5*7

81081=3^4*7*11*13

78975=3^5*5^2*13

1468935=3^6*5*13*31

6375105=3^7*5*11*53

436444281=3^8*7*13*17*43

PROG

(PARI)

isprab(v) = {my(sig = sigma(v)); if (sig < 2*v, return (0)); if (sig == 2*v, return (1)); fordiv (v, d, if ((d != v) && (sigma(d)>=2*d), return (0)); ); return (1); }

a(n) = {my(p = 3^n, k = 1); while (1, if (k % 3 != 0, v = p * k; if (isprab(v), return (v)); ); k += 2; ); }

\\ Michel Marcus, Mar 07 2013

CROSSREFS

Cf. A006038 (odd primitive abundant numbers).

Cf. A115414 (odd abundant numbers not divisible by 3).

Sequence in context: A017529 A321497 A335084 * A306497 A115414 A358412

Adjacent sequences: A133685 A133686 A133687 * A133689 A133690 A133691

KEYWORD

nonn,more,changed

AUTHOR

Pierre CAMI, Jan 04 2008

EXTENSIONS

Some terms corrected and more terms from Michel Marcus, Mar 07 2013

STATUS

approved