Related Clues:

• American with diamonds -- Detective Sergeant puts two and two together?
• Uses a four-function calculator, perhaps
• Goes on to say diehard's got no heir
• No need for dead ends or annexes
• Counts half of those in 21 down at school
• New contacts, informally
• Supplements with small advertisements getting centre spread?
• Performs some simple math
• Puts in; tacks on
• Tallies (up)
• Also mentions
• Poster vacant doofus puts together
• Offers further
• Uses sigma notation, in calculus
• Does some summing