RAPID CITY- Carl Albert "Al" Grimm, 91, died suddenly, early Tuesday, January 2, 2018 at Rapid City Regional Hospital.

He was born Apr. 1, 1926, in Cincinnati, OH, to Carl Hugo and Alberta (Kumler) Grimm. He grew up in Cincinnati, where he attended Withrow High School. Upon graduating in 1944, he enlisted in the U.S. Navy. After boot camp at the Great Lakes Naval Training Station, he served on two minesweepers in the Philippines, the USS APc-2 and USS YMS-334. After discharge from the Navy in 1946, he attended the University of Cincinnati, earning Bachelor's and Master's degrees in Mathematics.

In 1940, while on a family vacation, Al and his family were intending to stay at Cedar Pass Lodge in the Badlands, but the heat was oppressive. Told that it would be cooler in the Black Hills, they proceeded to Palmer Gulch Lodge near Hill City, where Al fell in love with the Black Hills and met his life-long friend Watson Parker. On Sept. 10, 1948, Al married Jeanne Irma Blase at Knox Presbyterian Church in Cincinnati. In the following summers, Al worked at Palmer Gulch Lodge. While there, he learned of a position in the Mathematics Department at South Dakota School of Mines & Technology. In the summer of 1952, Al, Jeanne, and their firstborn son moved from Cincinnati to Rapid City. There, Al and Jeanne were charter members and elders of Westminster Presbyterian Church.

Al especially enjoyed hiking, spelunking, and camping in the Black Hills. Al and friend Watson conducted many "explores" of Black Hills ghost towns and mines. He and his family spent summers camping in the Rocky Mountains of Colorado, Wyoming, and Montana, especially exploring old ghost towns and mines. He had a large model railroad, for which he had built detailed replicas of old Black Hills ghost town and mine buildings, which unfortunately was destroyed in the 1972 flood. He was an amateur astronomer and spent many evening hours gazing at the heavens through his telescopes. In his earlier years, Al was an avid and accomplished golfer, winning the Rapid City Golf Championship at Meadowbrook in 1970, but he later took up cycling. He was especially proud of having biked the entire 109 miles of the Mickelson Trail in both directions. He continued to ride his bicycle until after his 91st birthday.

At SDSM&T, Prof. Grimm was dedicated to teaching and research. His favorite course was differential equations. In 1975, he received the SDSM&T Good Teaching Award and, in 1983, the Presidential Award for Outstanding Professor. Although normally somewhat reserved, he became animated with enthusiasm when teaching students mathematics, no more so than his sheer delight in explaining the simple yet profound beauty of Euler's identity. His field was number theory, and he much enjoyed the mental challenges of pure mathematics. Probably his most significant contribution was a paper published in The American Mathematical Monthly in 1969 entitled "A Conjecture on Consecutive Composite Numbers," now simply known as "Grimm's conjecture." He continued to work on mathematical puzzles until his death.

Al retired from SDSM&T in 1988, and for the following 18 years he and Jeanne enjoyed many camping trips in their little motorhome, particularly to Capitol Reef National Park in Utah, and the Pacific coast of Oregon and Washington, often combined with visits to their children and grandchildren. Al and Jeanne instilled in their children a love of hiking, camping, nature, and of National Parks, Monuments, and Forests.

Al is survived by three sons, Eric C. (Jane Allard) Grimm, Jefferson, SD, David C. (Randi S.) Grimm, Sandy, UT, and Jeffrey H. (Christine Webb) Grimm, Albany, OR; six grandchildren, three great-grandchildren; and his sister Mary Carol Bangert, Carson City, NV. He is preceded in death by the love of his life, his wife of nearly 69 years, Jeanne, on July 28, 2017.

A service for family will be held later. A memorial has been established in the name of Carl Albert Grimm for the Mickelson Trail. Checks should be made payable to South Dakota Parks and Wildlife Foundation and mailed to 11361 Nevada Gulch Road, Lead, SD 57754-9801. Indicate that it's for the Carl Albert Grimm Memorial on the memo line of the check or in a note.