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A348749 Odd numbers k for which A064989(sigma(k)) > A064989(k), where A064989 shifts the prime factorization one step towards lower primes, and sigma is the sum of divisors function. 10
9, 25, 45, 49, 75, 81, 117, 121, 225, 243, 289, 325, 333, 405, 441, 529, 549, 605, 625, 657, 675, 729, 841, 925, 1053, 1089, 1125, 1215, 1225, 1413, 1445, 1521, 1525, 1575, 1665, 1681, 1737, 1825, 1875, 2025, 2205, 2401, 2475, 2493, 2601, 2817, 2825, 2925, 2997, 3025, 3033, 3125, 3249, 3481, 3573, 3645, 3675, 3789 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Sequence obtained when A003961 is applied to A348739 and the terms are sorted into ascending order.

LINKS

Table of n, a(n) for n=1..58.

Index entries for sequences computed from indices in prime factorization

Index entries for sequences related to sigma(n)

MATHEMATICA

f[2, e_] := 1; f[p_, e_] := NextPrime[p, -1]^e; s[1] = 1; s[n_] := Times @@ f @@@ FactorInteger[n]; Select[Range[1, 4000, 2], s[DivisorSigma[1, #]] > s[#] &] (* Amiram Eldar, Nov 04 2021 *)

PROG

(PARI)

A064989(n) = {my(f); f = factor(n); if((n>1 && f[1, 1]==2), f[1, 2] = 0); for (i=1, #f~, f[i, 1] = precprime(f[i, 1]-1)); factorback(f)};

isA348749(n) = ((n%2)&&(A064989(sigma(n)) > A064989(n)));

CROSSREFS

Cf. A000203, A003961, A064989, A326042, A348739, A348748, A348939 (terms of A228058 that occur here).

Cf. also A348742, A348754.

Sequence in context: A114057 A227518 A031036 * A291259 A051132 A247687

Adjacent sequences: A348746 A348747 A348748 * A348750 A348751 A348752

KEYWORD

nonn

AUTHOR

Antti Karttunen, Nov 02 2021

STATUS

approved

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Last modified February 5 03:48 EST 2023. Contains 360082 sequences. (Running on oeis4.)