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A326074 Numbers n for which A326073(n) is equal to abs(1+A326146(n)). 5
3, 6, 28, 221, 391, 496, 1189, 1421, 1961, 2419, 5429, 7811, 8128, 11659, 15049, 18871, 36581, 44461, 48689, 57721, 80851, 86519, 98431, 107869, 117739, 146171, 169511, 181829, 207761, 235421, 240199, 280151, 312131, 387349, 437669, 497951, 525991, 637981, 685801, 735349, 752249, 804101, 885119, 950821, 1009009 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that 1+(A001065(n)-A020639(n)) is not zero and divides 1+n-A020639(n).

Note that whenever n is even, then the above condition reduces to "(even) numbers n such that A048050(n) is not zero and divides n-1", which is a condition satisfied only by the even terms of A000396.

a(375) = 360866239 = 449 * 509 * 1579 is the first term with more than two distinct prime factors, the second is a(392) = 413733139 = 199 * 239 * 8699, and the third is a(485) = 718660177 = 41 * 853 * 20549.

Question: Are any of these terms present also in A326064 and A326148? None of the first 564 terms are. If such intersections are empty, then there are no odd perfect numbers.

If one selects only semiprimes from this sequence, one is left with 6, 221, 391, 1189, 1961, 2419, 5429, 7811, 11659, 15049, 18871, 36581, ... (555 terms out of the first 564 terms). Their smaller prime factors are: 2, 13, 17, 29, 37, 41, 61, 73, 89, 101, 113, 157, 173, 181, 197, 233, 241, 257, 269, 281, 313, ... while their larger prime factors are: 3, 17, 23, 41, 53, 59, 89, 107, 131, 149, 167, 233, 257, 269, 293, 347, 359, 383, 401, 419, 467, 503, 521, ..., and both sequences of primes seem to be monotonic.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..564; all terms < 2^30

Index entries for sequences where any odd perfect numbers must occur

PROG

(PARI)

A020639(n) = if(1==n, n, factor(n)[1, 1]);

A326073(n) = gcd(1+n-A020639(n), 1+sigma(n)-A020639(n)-n);

A326146(n) = (sigma(n)-A020639(n)-n);

isA326074(n) = (A326073(n)==abs(1+A326146(n)));

CROSSREFS

Cf. A000203, A001065, A020639, A048050, A061228, A325960, A325961, A326064, A326073, A326146, A326148.

Cf. A000396 (a subsequence, the even terms of this sequence if there are no odd perfect numbers).

Sequence in context: A220823 A024497 A007228 * A096155 A007452 A046981

Adjacent sequences:  A326071 A326072 A326073 * A326075 A326076 A326077

KEYWORD

nonn

AUTHOR

Antti Karttunen, Jun 10 2019

STATUS

approved

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Last modified January 28 00:32 EST 2020. Contains 331313 sequences. (Running on oeis4.)