A326074 - OEIS

A326074

Numbers n for which A326073(n) is equal to abs(1+A326146(n)).

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

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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