A234970 -id:A234970 - cp's OEIS frontend

A234969 Abundant numbers whose aliquot sequence is abundant, deficient, abundant, ..., etc.

220, 1064, 1184, 2172, 2620, 5020, 6232, 10744, 12285, 17296, 63020, 66928, 67095, 69615, 79750, 80535, 83655, 86086, 100485, 122265, 122368, 141664, 142310, 146344, 171856, 173500, 176272, 177340, 185368, 191260, 196724, 280540, 308620, 319550, 333920

Offset: 1

Michel Marcus, Jan 02 2014

nonn

All smaller members of an amicable pair (A002025) belong to this sequence.
Also abundant members of the sociable quadruple represented in A222977 are here.
Starting at k=3, I found 1, 7, 18, 63, 160, 331, 858 terms up to 10^k.

			The aliquot sequence 220->284->220->... has the requested form, so 220 is here.
1064 is here too since its aliquot sequence is 1064->1336->1184->1210->... .

Cf. A002025, A002046, A063990, A222977, A234970.

isAmicable(n)={my(a=sigma(n)-n); (a<>n) && (sigma(a)-a)==n;} \\ from A063990
isSociableADAD(n)={my(a=sigma(n)-n); if (!a, return (0)); my(b=sigma(a)-a); if(! b, return (0)); my(c=sigma(b)-b); if (!c, return (0)); my(d=sigma(c)-c); if (d != n, return (0)); ((n>a) && (ac) && (cb) && (bn));}
isok(n) = {my(oldn = n); my(newn = sigma(oldn) - oldn); my(dir = sign(newn - oldn)); if (!dir || (dir < 0), return (0)); oldn = newn; while (1, newn = sigma(oldn) - oldn; ndir = sign(newn - oldn); if (!ndir || (ndir == dir), return (0)); if (isAmicable(oldn), return(1)); if (isSociableADAD(oldn), return(1)); oldn = newn; dir = ndir;);}

cp's OEIS Frontend

A234969 Abundant numbers whose aliquot sequence is abundant, deficient, abundant, ..., etc.

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