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A359192
a(n) is the smallest square pyramidal number with exactly n prime factors (counted with multiplicity).
2
1, 5, 14, 30, 140, 1240, 4900, 10416, 85344, 173880, 1801800, 5559680, 44608256, 357389824, 44870400, 110099203200, 2861214720, 98269966080, 982218617856, 1466149724160, 11727587164160, 243912389529600, 750591347982336, 1951282875801600, 37635982963937280, 460962807482777600
OFFSET
0,2
LINKS
Eric Weisstein's World of Mathematics, Prime Factor
Eric Weisstein's World of Mathematics, Square Pyramidal Number
EXAMPLE
a(4) = 140, because 140 is a square pyramidal number with 4 prime factors (counted with multiplicity) {2, 2, 5, 7} and this is the smallest such number.
PROG
(PARI) sp(n) = n*(n+1)*(2*n+1)/6; \\ A000330
a(n) = my(k=1); while (bigomega(sp(k)) != n, k++); sp(k); \\ Michel Marcus, Dec 20 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Dec 19 2022
STATUS
approved