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A237352 a(1)=1; for n>1, a(n) is the smallest positive integer for which sigma(a(n)) is a proper multiple of sigma(a(n-1)). 1
1, 2, 5, 6, 14, 30, 66, 138, 210, 462, 930, 1974, 3810, 6510, 14322, 26670, 58674, 118110, 245730, 498666, 826770, 1720110, 3784242, 7617630, 15728610, 27524910, 53323410, 110100270, 218453970, 480598734, 853272210, 1877198862, 3413108370, 6772073070 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Subsequence of A090552.

The first term of A090552 that is not here is 11 since sigma(11) equals sigma(a(4)), so it is not a proper multiple.

LINKS

Hiroaki Yamanouchi, Table of n, a(n) for n = 1..50

PROG

(PARI) lista(nn) = {n = 1; precs = sigma(n); print1(n, ", "); for (n=2, nn, if ((((ns=sigma(n)) % precs) == 0) && (ns != precs), precs = ns; print1(n, ", "); ); ); }

CROSSREFS

Cf. A090552.

Sequence in context: A100630 A275839 A057302 * A109784 A221472 A076624

Adjacent sequences:  A237349 A237350 A237351 * A237353 A237354 A237355

KEYWORD

nonn

AUTHOR

Michel Marcus, Apr 22 2014

EXTENSIONS

a(33)-a(34) from Hiroaki Yamanouchi, Sep 30 2014

STATUS

approved

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Last modified May 24 23:45 EDT 2020. Contains 334581 sequences. (Running on oeis4.)