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A357921
Primitive abundant numbers for which there is no smaller primitive abundant number having the same ordered prime signature.
0
20, 70, 88, 272, 550, 572, 945, 1184, 1430, 1575, 2205, 3465, 4288, 5775, 7425, 8085, 12705, 15015, 16768, 24272, 28215, 47025, 49875, 65792, 69825, 78975, 81081, 103455, 131625, 152224, 153153, 182325, 189189, 266752, 297297, 342225, 351351, 363375, 387345, 392445, 474045
OFFSET
1,1
EXAMPLE
550 is in the sequence as it is primitive abundant and it is the smallest primitive abundant number having its prime signature (in this case (1,2,1)). No positive integer < 550 is a primitive abundant and has prime signature (1,2,1).
PROG
(PARI) upto(n) = { m = Map(); res = List(); forfactored(i = 1, n, if(!mapisdefined(m, i[2][, 2]), if(isA071395(i[1]), mapput(m, i[2][, 2], i[1]); listput(res, i[1]) ) ) ); res }
isA071395(v) = {if (sigma(v) <= 2*v, return (0)); fordiv (v, d, if ((d != v) && (sigma(d) >= 2*d), return (0)); ); return (1); } \\ isA071395 from Michel Marcus at A071395
CROSSREFS
Supersequence of A083873.
Sequence in context: A234367 A071395 A362053 * A335557 A245856 A053741
KEYWORD
nonn
AUTHOR
David A. Corneth, Oct 20 2022
STATUS
approved