portrait: 85

the product of two prime numbers (5 and 17), and is therefore a semiprime of the form (5.q) where q is prime. specifically, the 24th Semiprime, it being the fourth of the form (5.q). together with 86 and 87, forms the second cluster of three consecutive semiprimes; the first comprising 33, 34, 35. with a prime aliquot sum of 23 in the short aliquot sequence (85,23,1,0). an octahedral number. a centered triangular number. a centered square number. a decagonal number.