A222975 Smallest member of sociable quadruples with signature: abundant, abundant, deficient, deficient.

1264460, 2115324, 2784580, 7169104, 18656380, 28158165, 81128632, 174277820, 498215416, 1236402232, 1799281330, 2387776550, 2717495235, 2879697304, 15837081520, 17616303220, 91411869465, 111375706442, 661126361272, 741158497112, 1045805730255, 1092162882824

Offset: 1

Author

Michel Marcus, Mar 11 2013

Keywords

• nonn

Comments

Members of a sociable quadruple are usually listed in the order with which they appear in the corresponding aliquot sequence. Therefore, in a sociable quadruple the 1st member is abundant, and the 4th member is deficient. In all, we can get 4 possibilities, and a sociable quadruple can be (with A for abundant, and D for deficient) : AADD, ADDD, ADAD, AAAD. The numbers in these sequences have been voluntarily limited to 12 digits maximum, the current status of the exhaustive search (see Pedersen link).

Examples

			The first quadruple of this type is: 1264460, 1547860, 1727636, 1305184, that are respectively abundant, abundant, deficient, deficient.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..28
• Jan Munch Pedersen, Known Sociable Numbers of order four, Tables of Aliquot Cycles.

Crossrefs

Cf. A090615, A222976, A222977, A222978.

Extensions

a(21)-a(22) from Amiram Eldar, Apr 05 2024